Depends. I think a sump is worth it if you set the tank up that way to begin with, such as buying a reef-ready tank with a built-in overflow, etc. If you already have the tank and want to set up a sump, then you're most likely going to have to use a continuous siphon overflow and run some plumbing up and down the back of the tank, which to me seems like more trouble than it's worth, imo.