Except you can't shoot through them like you can a filter. Not too mention lens caps can be tricky to remove quickly, especially when buried under a deep lens lens hood like the one my 70-200; and that even once I do have it removed I then need to stow the cap in some fashion to free up my other hand for shooting because those big f/2.8's have caps the size of salad plates. If I'm shooting landscapes this scenario is less of an issue. If I'm shooting wild life it very much IS a an issue for me.
No offense to anyone intended here, but here's a radical thought: Maybe the person best able to determine if I need a filter on my lens, just maaaaybe... That person is me? And what if we extend that logic to, say... Everyone?
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