I use car covers a lot. I'm very big into detailing and up keep.

Another responder already mentioned a lot of good things. A car cover has saved me so many times it's not even funny. A car cover has saved me from hail damage on a Mustang GT convertible I have as a secondary car.
Neighbors and local dealers suffered massive hail damage and the Mustang had 1 noticeable ding and 2 very shallow dings. Other cars in the area look like they where hit with machine gun fire.

Don't buy the cheap kind. Make sure it's a soft thick material and it should fit snug on your car. You don't want it flapping around and rubbing too much and only use it if your car is clean.

Benefits...

Keeps car cooler.
No de-icing in the winter (ice collects on cover but you just roll it off).
Less washing.
Protects against bird poop.
Less likely to get stolen or vandalized (visual barrier).

What I do is roll it off from front to back and store it in the trunk or hatch. Rolling it on and off makes it real easy. Wash the cover while it's on the car.

So long as you don't choose a stiff cheap cover and make sure it's the right size for your car you should do fine. Benefits more than justify the costs.

On vacation at my Mom's in New Mexico it was snowing and in the morning everyone's windshields where iced over. Several people where de-icing and all I had to do was look at them and sigh then just roll off my cover and I'm ready to go. No ice.