I am a friend of the protective filter, and at least once I was such a part protects also from a bad injury on the front lens. He usually stays on it forever, except in special situations where additional reflections may interfere. But it makes no sense to destroy the image quality of a good lens with a cheap filter, so I'm ready to grab here somewhat deeper into their pockets.
Small drawback (but it can not filter this): Despite a very flat design, the vignetting increases slightly if you use a filter. This can, however, correct in the image processing.
