I clean it every time, several times before spinning the new filter on. It's a good practice to help ensure the old filter gasket didn't stick to the side of the engine. I also make sure the hollow bolt that holds the filter mounting plate and the filter screws on to is tight. I had it come loose on me a few OC's ago. Pre-filling the filter and oiling the gasket is just something you should never ever forget to do, even if you do work at a quickie lube place.