ONJ wrote:
So, if I get a sump for whatever reason, what purpose will it serve for me.
What would I do with it?
I do have a 15 gallon tank I could use I guess.

Try it without and see how it goes.

I think the advantages a

1) Place to hide all the equipment.
2) Usually have a Surface skimmer - prevent an oily film from collecting
on surface of tank.
3) Wet/Dry setup with bio balls or similar.
4) coarse filtration on the return
5) Increase effective volume.
6) Possible refugium partition.

I think sumps got started because of the wet/dry filter systems. These
need space for water to dribble over the bioballs which is inherently a
gravity type system. To prevent floods, it was engineered as under the
tank with enough volume to avoid overflow if the return pump turns off
(power failures, etc.). You could also do this above the tank with a
single pump, or even a two pump system if you don't mind the risk of a
flood if the return pump stops and the other keeps going.

I had a wet/dry filter until I ditched the bioballs (too much nitrates),
but I still use a sump for all my heaters, skimmer, reactors, etc and to
create flow from the return pump. I also have some coarse filter
material in the return that catches loose hair algae and uneaten Nori.

Is it required? Not at all.

--Kurt