dcollins said:
Cavalry charges are certainly the first to come to mind; the fact that the facing contradicts the actual size of quadruped miniatures is another.
The second part there is so minor as to be unimportant - all you need to do is put a bigger base on the mini.
The fact is, they
needed to make this change to be consistent with the rest of the 3e rules - rules like "there is no such thing as facing".
Really, the 'face' of a creature in 3.5 isn't where it is, it's where it
could be. It's a range of possibilities, like the "electron cloud" surrounding the nucleus of an atom. Since the D&D round is broken down into 6-second lengths, you don't know
exactly where it is at every point during those 6 seconds, but you know the general area, and that is sufficient.
As for cavalry charges, and other instances of "overlapping" squares, here's my theory (and we'll see if it's what's really in the books): Assume that tall creatures "really" take up 1/4 of their square at any one time, and long creatures really take up 1/2 of their square at any one time. (these are estimations for combat - you can pack more in but they won't be fighting effectively!)
Using these guidelines, you can overlap creatures - however, when you do so you decrease their ability to maneuver, and they lose their dexterity bonus to Armor Class.
If you're in a massed cavalry charge, you can't be making your horse dodge left and right, wheel around to avoid blows, etc. If you're fighting in a tightly packed phalax (4 people in a 5' square) and someone pokes a spear at you, you're not going to be sidestepping it - there's nowhere to go!
This probably belongs more in House Rules if there's going to be much further discussion of it, but it's certainly one possibility.