Both. If you start with just a simple sump you can cordon off some area for a fuge with egg crate (if you don't have baffles or add your own baffles). My sump is a converted ecosystem sump (came with my used setup) and goes sorta like this:
chamber for inlet, center chamber for miracle mud fuge, baffles, chamber for return
and I have it going like this:
chamber for inlet, center chamber, first section 15 - 20lbs LR and chaeto, egg crate baffle, skimmer, baffles, return
Not sure if that made sense, but hope it helps.