Adds a bit of weight to a band's sound without having to commit to changing the key (the singer might not be able to hit some notes if it's in E flat). Some songs just have a snappier energy in standard that just isn't there in E flat, maybe Dime was just trying to find a balance?
Megadeth did the same thing for their first couple of albums.
Some songs by Lamb of God, Avenged Sevenfold, Illnath, and some alternative bands use C#. I really like this tuning. It sounds a bit darker than drop D, but for some reason I feel it's also easier to play in.
My band Tadashi uses C standard and drop A# tuning on a couple songs. The rest is all drop D and E standard (which I prefer). I use 11's on the standard and drop D, 12's on the C standard / drop A#