Just one poor sucker's opinion here, but car covers (especially when used outside) often do more harm than good.
Pro: Sun protection
Cons: If you have any wind, they rub on the paint. If there is any dirt/dust/pollen/etc on the surface of your car, that rubbing is even more abrasive. They also trap moisture against the surface of your car, including moisture/vapor rising from the ground as part of the natural evaporative process.
I like to keep our cars under cover (i.e., in a garage) as much as anyone, but cars are designed to be in the outdoors. Millions and millions of them never see the inside of a garage and last for decades, especially if washed and waxed semi-regularly.