For a start, you can control temperature, pH, lights, pumps, powerheads, reactors of all kinds, top off, and the list goes on. The controller I have, the reefkeeper elite, and previously the reef keeper lite can do all of these. Other controllers like the apex and profilux can do even more! From dimming t-5s to naming outlets, they can do it all. So a controller is not a glorified timer, it is that and then some. I and many other reefers have found it to make maintenance a breeze, in fact with some controllers, you can do auto water changes, auto salt-creep correcting, and auto skimmate emptying (about as lazy as you can get, I know).