Many years ago we had issues with keeping all the cars clean, as we didn't like to use car covers. We were finding that the car covers were scratching the bonnet and the roof above the windscreen as we would pull the covers on and off (we like to look at our cars, so this would happen quite a bit!). In a perfect world, the covers should not do this, but over the years of being in a dusty shed (even the cleanest sheds get dust!), dirt would build up in the covers and finally begin scratching our cars every time we took them on and off. So nowadays, the only time we use a cover is short term - if a car is in peril (like being in a busy workshop) or for security, so no one can see what car it is under the cover.