i was asking this same question on here a couple months ago. the conclusion i came to is that i would use percussion loops but only as a background sound. then layer the main percs over top ei. kicks, claps, snares, hithats , cymbals, and shakers. i actaully swear by this technique now. i find it gets my tracks started way quicker. as for any other kinda of loop, i dont see the piont. maybe an FX or fill loop though but other then that i couldn't feel good about it. but like others have said do what you want, and if it sounds good its good.