We have used our TT cover because it helps keep the ice and snow from direct contact with the roof. It also keeps the dirt, leaves and pine needles off the roof.
The problem is we sometime leave for a week or so in the winter so we have to remove it.
Last year we parked the TT in November, then spent two week in FL in January, then went to KY in April. The weather in IN was mild so the cover was never installed.
I have found that proper fit and foam padding on sharp points such as the gutter tubes is very important.