I think this is a big issue, because you must do much more work when you are creating a resousepack. In Minecraft 1.5, it was like gethering textures and put it in a folder.... finished.
Today it gets more and more difficult to make a good looking texturepack (alt Blocks). And as Magnus said it is very laggy when you can't turn it off.
So I really hope this setting will be back in a future snapshot version.
Yeah! But I think it would be better when it is turned off by default and you may turn in on in resousepcks.
As I said the rotations are sometimes really ugly.
The performace drops are not only in the snapshot, when I play 1.8 without alt bolcks on laggs, when it is on the game is unplayable