for fat loss........i would say training abs is about as effective as training biceps. there probably about the same size of muscle (both biceps together), and since you cant spot reduce fat the only effective way to drop waist size is to decrease your bodies total fat....and since for every pound of muscle you gain, ur body burns an extra 100 calories a day, i would say that training abs isnt very effective, but will help a tiny bit if incorporated.
but thats all based on hear-say...as ive never tried to lower m,y bodyfat before
ROFL!! Thats been pretty obvious!!