That's actually a good point, there is already a killswitch for spells in the game. If you try to cast the same spell, it will cancel the spell you're casting. So in that sense, having to press enter isn't really necessary.

Still, I like it. I can't even remember how many times I cast the wrong spell in 11 because I pressed the wrong macro. This makes it more difficult to mis-cast, it's pretty convenient for me.