I used to cover mine. PITA to get on and off but manageable. Never had issues with it rubbing paint/gelcoat. Protected well enough and always looked shiny just like before I covered it.
The cons for me and why I stopped using it; The adco cover I had lasted 2 seasons before all the grommets pulled away from the fabric where the straps connected rendering it useless. Before it failed I had issues when it would snow and I wanted to leave for a trip, it's about impossible to get off. If you don't travel in winter this is not an issue.
I never really thought of snow as a threat to an rv, at least anything a cover would solve. I have learned not to park under my Locust trees in the fall as they make a horrible mess on the roof and a huge pain to clean. That is about the one and only time I would think a cover would have been really nice. I don't cover any more and I don't notice any difference in the finish. I do wax it 2x a year and have tire covers.
I travel frequently (at least once a month) enough that getting a cover on and off just wasn't worth the hassle.