My thesis is that there IS a "correct" or "best" number of units for a wargame, and too little or too few is a bad thing.
First, some home made definitions:
Unit = a miniature or group of miniatures or stands ("elements") that maneuvers together and fires together as a group. In effect, they are a single entity although they can be made up of many elements. They tend to either be kept a in "coherency range" of 2-3" or kept on a movement tray to keep them together and distinguish their "togetherness."
Element = this is either a single miniature or a Flames of War/DBA type diorama base with miniatures fixed onto it.
My suggestion is, no matter what the "scale" or "level" of conflict the wargame represents, be it 1:1 squad level skirmish, platoon level, company level, battalion level or even division level, there is only so many units a wargamer can comfortably handle. Too few units and the game becomes lame or simplistic. Too many and the game bogs down without any extra tactics or strategy being added.
Imagine a game where each side has a single squad of 10 men. That squad travels in a group, moves and fires as a single entity. The 10 men are a single unit. The game is essentially a 1:1 duel between two units. The game will not have many tactical choices (decision points). There are not enough units to make it interesting. Now imagine the squad of 10 has been broken up. Each miniature can maneuver and attack separately. There is now ten units per side - as each soldier is his own "unit." Obviously, there are now a lot more decisions to make.
But there is a point where more units do not add more decisions and the game bogs down. Let's say the game is a company level one. You could have a game with 90 troops, each moving and firing independently. That would be, in effect, 90 units. A bit crazy. It makes more sense to collect units into, say, 9 squads of 10 - reducing the number of independent units to 9. It's also very unrealistic and unhistorical to expect a commander to individually micromanage the individual actions of every single one of those 90 men.
How many units here? If the space marine squads move independently, there are three. If they act together by platoon, there is only one unit.
I don't want to confuse the argument...
Now, the point a game "bogs down" can also vary wildly depending on the complexity of the rules. A game of Infinity can be slow with only 15 minis if they all have complex special rules. A game of LOTR can handle more in a fraction of the time. This is not amount of units vs time. Because that depends on how the rules were written and is impossible to "prove."
What I'm trying to focus on is the amount of units vs the tactical choices. With only 1 unit each side (even if they have 10 men in them) if they move and shoot together as "one" you have a 1:1 duel. The 10-man unit could equally be represented by a single man, with 10 hitpoints.**
So we understand a "unit" can take a lot of different forms: single guy, a bunch of guys which move in "cohesion", a movement tray with 20 guys... so what IS the "perfect" amount of units?
Well, I'd say you need at least four units, preferably five or more.
Let's look at historical examples of what was "manageable."
If you think of ancient armies, there was often a right flank, left flank, centre, reserve, and maybe a skirmish line and cavalry element (usually on a wing or both). That's 4-7 independent "units."
In a WW2+ platoon, there's three squads, divided into fire teams, (6?) with maybe a HQ element and maybe transport vehicles. Depending on how they are divided, that's 4-10 units.
A naval task force might comprise of a amphibious assault ship, a destroyer, a submarine, a few frigates and a supply ship. That's 5-6 units.
A fighter squadron of 12 might be divided into pairs or finger fours. That's 3-6 units.
A lot of wargames allow players to micromanage to an unhistorical and unrealistic extent. A WW2+ company commander might control 3 platoons (9 squads), a HQ element, and maybe 2-3 attached heavy assets. However he likely only manages the platoons or at lowest, the squads - he doesn't interact with each individual fire team or direct the fire of individual soldiers. So he in effect controls 5-7 units, not the 40 or so sub-units that actually exist in his force. Allowing players to mico-manage at command levels far below their "level" is a trap a lot of wargames fall into, and creates many more units than are actually needed.
So about this mystical "perfect number" of units in a wargame? I'd say 5-12 "units".
In a game like Tomorrow's War, this would be six units. The troops are grouped into three units of four, but each vehicle would be a separate unit. Also, I wanted to show off my $2 sci fi APCs from the junk shop. Many Hotwheels-scale cars scale well with 15mm.
Your reasoning, sir?
Well, many military organisations tend to historically divide into 3-5 units, be they squads in a platoon or divisions of WW2 warships. Besides, common sense.
An army made of a single unit isn't very flexible. A two unit army is also very simplistic. Three is the bare minimum for pinning, flanking etc. Four or five units you're starting to get more options - like even ancient armies had - you can have some sort of HQ/reserve and perhaps a scouting or specialist unit.
I've noticed any wargame which only has 3-4 units or less tends to rely on gimmicky rules or mechanics to add interest, be it resource management or special abilities/attack combos - and not on traditional wargame maneuvers.
Now, what about the "maximum"?" Assuming you also can "macro manage" one command level below, traditional armies could potentially divide into ~9-16 sub-units if you include the tier below.
Is there any strategies you could execute with 16 units that you couldn't also perform with 9-10? I'd suggest anything reliant on the successful actions of more than a dozen units acting independently is overly complex (and likely to fail). I like 12 as it's divisible in a range of ways. So there you go.
Furthermore, if you look at commercially successful rules, I'd say 90% fall into this bracket. 40K? Warmachine? Flames of War? Infinity? W-Wing? Check, check, check.
Conclusion: 5-12 'units' is the best size for a wargame, no matter what the command level it is at.
Gees, you wasted a lot of ink discussing something that seems rather obvious....If I only raise the awareness of this, I've accomplished my objective. The question:
"How many units do I expect to see on the table?" is an important one when you design your game.
I think it ties in closely with the questions "what command level is this game aimed at" and "am I choosing to give players the ability to micromanage far beyond the historical norm?" - which is perhaps grist for another post.
**This is why I have gravitated towards skirmish over "big battle." Friends used to play Warhammer Fantasy. They would lovingly paint "trays" of say, 20 Skaven each. Their army might have 8 trays of Skaven - 160 models to paint. In game terms, they merely had 8 units. The 160 Skaven were simply glorified hit markers. Whereas in Mordheim, you could paint 8 Skaven and have 8 units. Skirmish gaming provided twenty times less painting for the same amount of units.