They look kinda silly when they're superfluous or a belt would look better. With casual clothing they definitely look better with more relaxed comfier fits. With a formal suit they're a must.
I'm pretty new to /fa/, but what sort of look are you going for? Do you look like a stick? Or do you dress to look a bit more proportioned instead of all sleek like?
If you're shoulders are wide enough, a bigger looking ass isn't an issue. With decently sized thighs of course...