Keeping combat straight can be tricky. When everyone at the table agrees to keep things loose, it’s possible to forego maps and rely on oral description of what’s going on. And, of course, the system can help this; I can hardly imagine running a Ghostbusters combat using minis, for example. It would destroy the flavor of the game. If the game and the social contract allow for it, abstract combat can be much less of a headache.
In a more simulationist game, it can be more difficult, but still possible, to play without minis. My most recent session of Blade & Crown was a fight with a dozen or so combatants, PCs vs. bandits. We managed to run the whole thing abstractly, without resorting to a map. There were several moments where we nearly decided that abstract wasn’t working, but in the end, we managed to keep it fairly clear in all our heads.
The biggest need for minis, I think, comes from disagreements about who is where, and what they can do. And disagreements almost always seem to come from different people at the table having different conceptions of the topography. Not to say that anyone is willfully misconstruing anything; I think I’ve only encountered that a few times in my gaming. But when the GM says “There’s a lantern in the middle of the room”, some of the players may be thinking of a standing candelabra, while others may be thinking of a chandelier suitable for swinging from. Drawing a map can sort those kinds of problems out instantly.
They can also serve to muddle things further, but maps usually do more good than harm, in my experience. An important consideration is that different people process information differently. For some people, a map makes everything clear; for others, a purely oral description is best. But by relying on purely oral description, you’re limiting the modes of communication to just one, and whichever of the players process information visually are then likely to lose out on something.
Another reason for minis is what I’ve dubbed the Three-Body Problem of RPG combat. The original Three-Body Problem, of course, describes the difficulty of predicting the positions of three bodies acting on each other through gravity. In RPG combat, we’re talking about the problem of showing how three (or more) combatants change in relative position to each other.
Many games keep combat mapping abstract by using a linear graph. Agon, for example, and 3:16: Carnage amongst the Stars both do this, with variations. The trick is, though, what if someone wants to move perpendicular to the axis between other combatants? If, that is, Alice wants to move away from both Bob and Chris? A linear system can fall down when trying to represent this. And trying to represent sneaking around someone in a linear graph system can be a headache in itself. That’s the Three-Body Problem of RPGs.
The system used by Warhammer 3E is a nifty blend of abstract linear and explicit mapping. In it, you place counters for combatants on the table, and then place range markers between them. So, for example, if Alice wants to move away from both Bob and Chris, you place extra range markers between Alice and Bob, and between Alice and Chris. It seems to work well (though I haven’t had a chance to actually play it yet).
There’s a way to do this without buying Warhammer, of course; just use glass beads for range markers. Or, if you prefer, use dice. A D20 works nicely for this, as long as ranges aren’t too high. If the D20 sitting between Alice and Chris says “17”, then they’re 17 hexes apart. (Or feet. Or whatever.) And you could even use different-colored dice to indicate especially large ranges: “Red D20 = tens of yards, blue D20 = single yards”, for example.
The thing is, of course, once you get dozens of range markers or dice on the table, along with markers for all the combatants, it can almost be easier to just break out a map and minis. And then, the GM is more likely to describe that lantern clearly.