Lens covers for scopes can protect the primary lens from scratches and other types of physical damage. They also work well to keep snow, rain drops, etc. off your lens. If you buy the flip-up models and they have snow/rain on them, just flip them up to get a clear view of your target. Even if they are not the flip-up type, I'd much rather wipe moisture off the cover than from the actual scope lens--less damage that way.
I think the cap I use on my front lens is a Butler Creek flip-up style. I only use it when it is snowing, blowing snow, or if there is light rain. I usually don't go out when it is raining, but carry it in my butt pack if it looks like it is going to rain so I can throw it on if it does start to rain.
I'm not sure of the benefits of polarizing lenses, but I'm sure they would help cut down the sun's glare.
