There are members here who like to run an air stone in the tank or in the sump. The only downside is additional bubbles in the system and the salt creep can be really bad, but there are some reefers that put a value on running them, for good gas exchange, obviously.
I agree with above, a protein skimmer is another great way to get good aeration, and since I believe the vast majority of reefers do not use an air stone (and most do use a skimmer), I believe an air stone is firmly optional for most display tanks. An air stone may well be mandatory if a fish needs to be medicated, so not a bad thing to have a pump and air stone on hand