1 unit per tile is very much like what existed in Civ and civ 2. From a defender's point of view, having several units in one tile was suicidal. Except, and that's a big exception, in cities. I wonder whether the one unit per tile limit will be valid in cities too.
In Panzer General and other similar games (fantasy general, battle for wesnoth, elven legacy...), the limit is not an issue, it makes the game more challenging tactically, although sometimes you can have issues maneuvering your troops through chokepoints.