Many tanks have wave makers but probably a lot more don't. You have to look at your own tank conditions to see if you are among the ones who would benefit.
They add movement to the water (which some fish prefer greatly) and water movement can be beneficial in a lot of bioload circumstances. (See the 2 posts above mine.) For example, if I had a tank that had a large bioload or I was regularly vacuuming a lot of food / waste from the substrate, I would absolutely look at this option.