I think it probably reduced the amount of pixels it had to show, since there were less enemies on the screen and it only displayed them from the chest-down. It didn't work as well in huge battles, though, like the last ones.
Not pixels, but likely number of bodies. Pixels remain the same no matter what, but if there's only 25 enemies on screen and the game knows that what the rest don't matter, it only has to do rendering for those 25, as opposed to... I dunno, 200 (175 of which are off screen and don't contribute to the scene as viewed).
Huge battles though, I suppose that in certain circumstances, they might have a hard cap on the number of enemies active. Say, if the screen can hold 1000 enemies, but we know that the machine can't handle that many, we can limit it to, say 100 enemies (starting with the closest to the player). Everyone isn't even shown, they can't attack, people pass right through them... but if you kill someone, we'll activate another enemy somewhere (and hopefully in a manner so that you don't notice). Guess what, if your screen has 200 people on it no matter what, you're not going to see any performance gain.
'Least, that's how I'd do it. Maybe they know something else.
Oh, and welcome by the way. ^^
