really depends on the fish you keep. some fish probably don't move more than a few feet from their homes throughout the course of their entire lives. Others, like tangs (srry. dun mean to sound like tang police here) need plenty space to swim freely in the wild, which unfortunately we cannot replicate in our own homes.
since we are all already into this hobby, what we can do now is to try our level best to create a 'home away from home' for these fish, simulating their natural habitat, foods, etc in our own tanks. at the same time making our tanks more of a pleasure to view.
happy reefing.