They're great for stirring the sand. You won't be able to keep anything on your sand bed however. They will move or bury it. Sometimes they'll also swim up with mouthfuls of sand and dump them on your rocks. I've only had 1 out of 4 do that but it was quite annoying. Now my lawnmower blenny does it instead...haha. They can also get aggressive with other fish that may hangout in their level of the tank (hawkfish, blennies, other gobies).