Bigger would always be better but for one mechanic in Stellaris, that is empire sprawl. Every system, pop, district and colony you control adds to your empire’s sprawl. When your sprawl exceeds your administrative capacity that will increasingly apply inefficiency to your technology research, leader upkeep, campaigns and tradition adoption. This mechanic of diminishing returns leads to two distinctly different play styles, wide and tall.
The wide playstyle embraces sprawl inefficiency like a friend absorbing everything it can heedless of the diminishing returns. The tall playstyle dines like a gourmet only picking the very best and shunning the crud. It is acutely sensitive to sprawl inefficiencies. Wide vs Tall is a quantity versus quality dichotomy.
There are some misunderstandings about the true nature of the tall play-style so we will clear that up first.
Administrative capacity is deceptive. There are technologies, traits, edicts and jobs that can increase your administrative capacity and so reduce the cost of sprawl on your tech and traditions. However all those measures for increasing administrative capacity have some cost associated with them too. So an investment in increasing it is simply transforming your natural sprawl inefficiency into a different form of inefficiency. Bureaucrats can increase your administrative capacity but if they were not bureaucrats they could be cranking out research and alloys instead. Increasing administrative capacity to compensate for sprawl is substituting one inefficiency for another.
There are Stellaris gurus that will tell you that by increasing your administrative capacity you are playing tall. They would be wrong. If increasing your administrative capacity is bringing more benefit than it costs then you are already playing wide. A truly tall empire is one that would regard an increase in administrative capacity as a bad investment and avoid it. A truly tall empire does not incur the sprawl in the first place. A tall empire gets the resource benefit without the sprawl cost.
There are Stellaris gurus that will tell you that by building up pops in preference to acquiring systems is playing tall. They would be also wrong. Pops also increase your sprawl and their productivity is not necessarily better per unit of sprawl than a system. Indeed pops can even have negative productivity if they are unemployed. There are no unpopulated systems no matter how poor than will do that. In addition there are some systems whose raw benefit is far in excess of anything even the most efficiently employed pop can produce. A hypothetical empire composed only of such super systems would be the tallest of the tall even if it had no pops at all.
Forget increasing administrative capacity, all that does is exchange one efficiency for another. Forget preferring pops over systems, all that does is exchange one type of sprawl for another. What really distinguishes a tall empire from a wide one is the average ratio of resources gained per unit of sprawl incurred. Tall empires get a lot for little sprawl while wide get the opposite. Resources could be energy, alloys, research, fleets or relics and sprawl could come either from pops or systems. This ratio will be now be referred to as Sprawl Efficiency.
There is nothing on your user interface to tell you this ratio directly. You have to work it out as you go. For systems this is easy to work out because they each cost a flat 1 sprawl and their base production does not vary according to vagaries like happiness, stability and many other competing factors. Consequently we can readily evaluate whether a system would keep us tall or make us wide simply by looking at the quantity and value of resources to be found there. A system with only 2 units of energy would only give us 1 unit of energy profit after upkeep (ignoring capital costs building the station, the outpost and the influence spent on the system) for 1 sprawl. A 1:1 sprawl to a basic resource ratio is almost as bad as can be, only the widest of the widest should want such a system. However a system like the Tiyanki home system can yield 30 research for that same 1 point of sprawl. Even the tallest of the tall should be happy with such a system in its portfolio.
Systems with such rarities as the matter decompressor are the pinnacle of sprawl efficiency. At full development a decompressor will produce 2000 minerals for just one sprawl. Of course significant investments must be made to unlock that though.
Working out this ratio for pops is very complicated however. Pops incur sprawl from four different sources: themselves as a pop, the districts they live in, the colony they live in and the system they live in. This means that a given pop can cost you a very variable amount of sprawl depending on where and how it is employed. Your first and only colonist on a new colony alone in a new system would cost a whopping six and half sprawl even while producing absolutely nothing. In contrast your 200th pop on a ringworld barely costs more than 0.5 sprawl even while potentially being really quite productive (assuming he is not unemployed).
It gets even more complicated when we consider that many pops require other pops to support them in the form of amenities or consumer goods in order to produce anything. We might like to think a researcher gives us 12 base research for 0.5 sprawl but how many pops had to exist providing him with consumer goods, food and amenities to produce that? And what do those support staff add to the sprawl? Living standards, ethics, traditions, civics all have some impact on the sprawl to production ratio for different jobs on different planets too. This all makes for a very complicated analysis but there are some generalities we can draw for going tall with pops.
The base sprawl cost of a colony is very high at 5. This means we should try to have a given amount of pops concentrated in as few colonies as possible. Ecumopolis and Ring Worlds have the greatest potential for sprawl efficiency because of their higher potential capacity while small planets have the worst. That only works if you actually fill them with pops though, an empty Ring World is as exactly as inefficient as an empty small world.
Since habitability affects the productivity of biological pops but does not reduce sprawl we should also prefer high habitability. This is another benefit of Ring Worlds. This is irrelevant to robots though.
Since a colony must reside in an owned system there is a system cost too. A system can potentially house many colonies though so there is a sprawl efficiency in concentrating your population into fewer systems but since the system cost is very small compared with a colony cost it is not a huge concern. Three size ten worlds in one system (sprawl 5 x 3 + 1 = 16) is not better than two size fifteen worlds in two different systems (sprawl 5 x 2 + 2 = 12). Fewer colonies is much better than fewer systems.
Districts also cost sprawl but buildings do not. Consequently pops that live and work in districts instead of buildings are less sprawl efficient. A worker on a typical planetary mining district costs 1 sprawl, half for himself and half from the district even before looking at amenities and other considerations and assuming the mining district is working at capacity. If he was the only miner in that district then his sprawl would be a substantial one and a half. In contrast a ruler pop or a soldier that lives and works in a building will not incur a district cost and so would only cost a base 0.5 sprawl.
Also districts cost sprawl even if empty! An economic strategy that revolves around having spare capacities in districts is less sprawl efficient than one that aims to have only as many as needed.
Buildings incur no sprawl but a given number of population is needed to unlock a building slot and for low level buildings that is more population than the building can house and employ meaning some pops will have to be housed and employed in districts to enable it. Upgraded buildings can create jobs or housing for more than enough population by themselves to unlock the next building slot with little or no support from districts. So higher tier buildings are indirectly more sprawl efficient than lower tier ones.
Housing districts are generally more sprawl efficient than resource districts because they can house more pops than a resource district can house and employ. So providing you can make a building to employ your pops it is more sprawl efficient to house them in housing districts than house and employ them in resource districts. This makes most specialist jobs more sprawl efficient than most worker jobs because they can work in a building. However clerks and soldiers are pretty good for workers because they also have a buildings to work and the soldier gets housing with his job.
To illustrate the above: 8 alloy workers housed in a city district but working in a tier-III alloy building will cost 8 x 0.5 + 1 = 5 sprawl whereas 8 miners housed and working in 4 mining districts will cost 8 x 0.5 + 4 x 1 = 8 sprawl. If we assume that 1 alloy is worth 4x as much energy as a mineral then the miner will produce a surplus value of approximately 3 energy while an alloy worker will produce a surplus value of approximately 4 x 3 – 7 (6 minerals + 1 food upkeep) = 5 energy. Of course a tier-III alloy building also have a upkeep in volatile motes which are rare and valuable.
Overall we can say as a crude rule of thumb that rulers are more sprawl efficient than specialists who are in turn more sprawl efficient than workers. However there are innumerable factors from traditions, traits, ethics and civics affecting productivity and districts that can alter that balance.
If you play tall you want to have the maximum amount of resource for the minimum amount of sprawl. The trouble with pops is that even assuming you can employ them and do all the things to keep them fed and happy there is not much you can do decouple their sprawl cost from their productivity. More productivity will mean more pops which will mean roughly proportionately more sprawl. My best estimate is that pops can achieve an optimal average ratio of sprawl to product of 10 energy to 1 sprawl.
In contrast systems cost the same sprawl regardless of their productivity so if you can monopolise the very best systems you can make dramatic differences to your average sprawl to productivity ratio.
There are productivity multipliers for workers from technologies but they also exist for mining and research stations.
A true tall strategy would get its power from sources with minimal sprawl. The perfect tall strategy would get its power from sources with no sprawl impact at all. Are there such things in Stellaris? Yes there are.
Leaders are an asset for your empire that are completely sprawl free. You can have as many leaders as you can afford to pay and your sprawl will be completely unaffected. In general leaders are force multipliers which means they give you nothing in themselves unless combined with another asset. Admirals make your fleets better, Research Leaders make your researchers better, sector governors make your sectors better. There are some hard diminishing returns from having better leaders which are force multipliers because you will only have so many fleets and so many researchers and so many sectors.
However there is one leader which is less of a force multiplier and more of an asset in himself and that is the Explorer leader who pilots your science ships. Science ships can survey systems, investigate anomalies and excavate relic sites. More science ship with better leaders will mean more systems surveyed, more anomalies investigated and more relics harvested. All these activities can directly create material benefits in the form of access to better systems to claim, technologies, resources and ships but with no significant sprawl cost attached.
It should be noted that Leaders are an asset whose efficiency is impacted by high sprawl as sprawl increases their upkeep.
Envoys cost no sprawl but they can obtain for you material benefits in the form of commercial and research pacts which also do not increase your sprawl. They can help you develop your federations faster. A tall strategy could certainly employ more envoys.
Vassals and Tributaries supply their overlord with military and resource support for no cost to sprawl. Certainly a tall military power would look to maximise the number and quality of vassals and tributaries. It might be argued that in order to get vassals one must have considerable fleet power however as we will show fleet power is really quite decoupled from sprawl too.
Fleet power comes from a combination of admiral skill, technology, naval capacity and energy and matter resources needed to build and upkeep them. It is possible to acquire all these things with minimal sprawl footprint.
A basic starbase with just one anchorage can increase your fleet capacity by four. Although it must be situated in an owned system with a sprawl cost of one, it could also be a citadel with maxed out anchorages and a fleet logistics building increasing naval capacity by 36 in a system you wanted anyway because of its rich resources.
The materials that make the fleet could have come from hundreds of miners at enormous sprawl cost but they could also come from a matter decompressor or a bunch of tributaries at virtually zero sprawl cost.
Fleet power is an asset with a very high potential for being sprawl free.
It has to be said that influence is a resource in itself. It costs no sprawl and while there are not many ways to increase it but many ways to spend it none of the few ways to get extra influence have any sprawl implications.
A tall strategy has the potential to save influence through having fewer though better quality systems. Saved influence can be spent on force multipliers in the form of edicts and decisions. Influence stockpiles can also be utilised to lay claim to very valuable systems relatively distant from your borders.
If you have some fleet power you could hunt space fauna such as the Amoeba and Tiyanki for rich rewards at no sprawl cost.
Unlocked traditions are sprawl free assets that tall empires will tend to get earlier than wide empires since tradition adoption cost is one of the things adversely affected by sprawl. Traditions are bought with unity which is a resource that tends to come from pops and colonies though. A tall empire might look towards those rare sources of unity which do not come from pops such as minor relics found by leaders.
Given that tall empires should leverage the power of leaders above most other resources then any trait or civic that improves leaders are extremely suitable. Good leader traits are Venerable and Enduring which lengthen their lives, Quick Learner which help them level up faster and Talented which raises their level cap.
For civics you could look at Distinguished Admiralty for a militaristic tall empire and Meritocracy for a more general buff to leaders. Mega Corps lean towards tall by default but for a leader buff they have Ruthless Competition. Tall machine intelligences should look at Delegated Functions and Factory Overclocking. Hive minds have One Mind and Pooled Knowledge.
Other civics that could have potential for tall empires are those that give more or cheaper edicts such as Imperial Cult and Cut Throat Politics.
Civics like Diplomatic Corps and Public Relations Specialists which give more envoys are also good for a tall empire.
Questionable traits or civics for a tall empire are those that tend to facilitate or encourage sprawl through population growth. Rapid Breeders in particular is terrible. Conversely so called negative traits which do the opposite such as Slow Breeders are probably secretly beneficial for tall empires. The slower your pops grow the less they drive up your sprawl and the easier it is to keep them employed.
Civics which buff bureaucrats or reduce the cost of districts are there for the wide empires. Tall empires have no use for them.
Since the higher strata of pops tend to be more sprawl efficient than lower ones it might be that a tall empire could use civics that give extra ruler jobs or buff their output. Conversely civics and traits that encourage the reliance on low tier jobs are maybe less useful.