Because one day I was writing a fiddly algorithm that used lots of the same ol' for(long i = 0; i < limit; i++) loops and got fed up with typing them, so I made a quick macro. It ended up being so convenient that I put it in my globally-included "insanity.h" header, and now I use it constantly.
C is nice in that it lets you make simple improvements like this without some insane, obtuse coroutine-generator-iterator-factory-object nonsense.