In bigger fighting games like Tekken ( one of the new ones ) I usually don't learn any combinations. There I'll just be mashing, but in fighting games like SnkVSCapcom on the Neo Geo Pocket ( Haven't tried the one for the 'big' Neo Geo ) I'll learn the basic key combos ( in that example: Left + A, Left + B, Right + B, Right + A ) and use them.
If I'll have to press up, up, a, b, b, down, b to make an attack, I won't use that.
Cheers, Dave