Wavemakers are designed to give your aquarium the simulated effect of wave motion that your saltwater animals have when in their natural environment. They can also help flush out detritus (non-living particulate organic material) and accumulated waste in spots of your aquarium that don't get movement. The wavemaker will stir this waste up and allow it to be filtered.
Your fish will enjoy the water movement and currents and give them a chance to be active. Corals are stimulated by the current and water movement, this also brings the food TO them keeping your corals active and healthy. Also a wavemaker will stir up the sand in your aquarium releasing microscopic particles and organisms that your corals an inverts can feed on.