It's an interesting point some are making about it allowing the strengths/weaknesses of certain units to be used more, but that's not how it works with real armies - cavalry isn't is able to go out and face just infantry (for example), they'll have to deal with an army made up of combined infantry, pikemen, archers, etc... the whole point of combined forces is the units support each other
so I vote no...
it would be interesting to limit the number of units that can be on one tile, but a single unit per tile is a bad idea. What would be even more interesting is working in some way to figure out supply lines, so you can have as big an army as you want as long as you can supply it, and of course protect those supply lines against the enemy. Would make invasions much more interesting on both sides
maybe that's all been said before, I didn't read the whole thread