You're going to get varied responses, and some completely opposite of my experience. These days I'm fortunate to have a garage, but I have been through the days of park-it-outside... Based on that, I'd suggest only using a cover if you have to park where there are lots of bird bombs, nasty leaves and flowering trees that eat at your finish if left for any length of time, or use the cover only on a dry and clean ride -- never one you've driven and has dust or grime in it.
The challenge is, if your finish has some amount of dirt, and you put the cover on, fine, but some of that dirt will stay on the inside of the cover and begin a slow build-up, and every time to take it off then put it back on, you will ultimately introduce micro scratches... No way to stop it, no matter how careful you are. If you have a darker, aka esp. Black, finish, you'll see the evils faster than say on silver or perhaps pearl white. Other consideration is the type of cover you put on... Cheaper ones that don't breath will be an issue if there is any moisture on your finish, and it can sweat causing finish problems if the cover is on long enough. If you do go with a cover, my recommendation is ONLY get a high quality multi-layer one that breathes and will be OK If it rains while your cover is in place. The cover also needs to be custom for the MS, not a cheaper parachute sorta thing that will blow in the wind and cause different problems with your finish.
After all of that, and honestly, I'm not trying to do a bunch of scare tactics, when I used to travel frequently where there were a lot of pine trees and sap, I had a cover I used for that purpose, as I considered sap on my finish a worse thing than the smaller number of micro scratches I would probably introduce with just occasional use. If I didn't have the bird/bug/tree problem today, and was in your situation with a new MS, I'd live without a cover, and instead immediately put a coating on my ride soon after delivery... The coating will take the brunt of the elements, and you can have that redone if you need to in a year or two by a good professional... You'll have to live with a little bit of a dirtier car, but it will look good without a bunch of micro scratches, and your finish under it will still be OK. Id also have a good interior sunscreen I'd put up for my windshield, especially in the hotter times of the year to help protect that dash. I'll leave it to you as to if addition window tinting may be a good idea -- like with car covers, even more opinions on that.
Good luck.
