If you clean it everytime you change oil (2) things will happen-you get more dirty oil out, and if a problem is starting to occur (large pieces of metal in screen), maybe the problem can be caught before a more expensive (lock-up) happens. Honda used to do this same practice on engines. They did it to keep larger pieces of metal out of bearings, oil pump, etc. because some metal flashing can come loose from engine castings. Its too bad they didn't incorporate an oil filter instead-but there are lots of old hondas still running that had this set-up...