Another thing not mentioned is long-term filter flow.... If you have a 55g tank and a filter rated for a 60g, you're going to have to be religious in your maintenance because flow will gradually reduce due to detritus build-up. If, like Cornstar, you have a filtration capacity well in excess of your tank size, some reduction in flow isn't a concern, and full dissembly & clean-out of the system isn't required quite as often.