By clean-up crew people mean little herbivores and scavengers that keep the tank free of algae, uneaten food, etc. such as crabs and snails. Should you get a clean-up crew, well that depends on what types of fish are in your fowler(no puffers, eels, triggers, or other crustacean eating fish), and if you need any help keeping the tank clean.
I run mostly blue-legged hermits and astrea snails in my 29. I would recommend you pick some up. They are not expensive, and I find them more entertaining than the fish. I also have a chocolate chip starfish in there, but he may have to go as I try and grow my coralline.