It all depends on what kind of corals you are keeping. A friend of mine can NOT keep LPS in his system. He overskims, the tank is barebottom and he has a ton of flow. He WAS primarily a SPS keeper, then downgraded his lighting and circulation to help lower energy costs. LPS barely extend due to lack of nutrition in his overly-clean arrangement. He is now back to keeping SPS and the system is thriving again. IMO you CAN overskim a system to the point of stripping the water completely of non-photosynthetic nutrients.