A sump, IMO, is just a place to hold more equipment.
Per-se, it's not really filtration.
But I sure like the fact my heater, my skimmer, any carbon/etc I'd decide to run are all hidden under the stand.
Personally, a skimmer is the only real `filtration' beyond live rock I run. No cannister or other filter ... so I suppose you could run with a hang-on skimmer [just would need to sacrifice tank-space for the pump, input/output]