I don't think there is a single universal answer.
For us our canvas guy refuses to put covers on. Why? Because we are in an open windy mooring field and on a mooring. This can create abrasion & chafe and micro-scraching of the glass from the winds.
I was doubtful and wanted to see for myself so did my own experiment.. We had purchased a brand new Catalina with brand new dodger and canvas with window covers. We used only the middle window cover. After just one season the middle window was in worse shape than the two side windows. My canvas guy was right, for our location..
Now with that said, if at a dock, protected from winds and in an area of high UV then I think covers can make more sense. For us on a mooring in a windy anchorage with good fetch you could not pay me to install window covers.
Year six, no covers, exposed to the elements mid April to mid to late November each year.
My rules for care:
No one touches the dodger glass with fingers, body or hair.
No spray suntan lotion allowed on-board
No spray bug-dope allowed on-board
Dodger windows are only ever touched with a brand new fresh out of the bag microfiber rag. Used rags NEVER touch the windows nor do cotton or paper towels etc..
IMAR products are the only products to ever touch our windows.
I take clear dodger glass seriously especially with the number of lobster pots on the Maine coast
I learned those rules from my buddy Norm and thank him every day I can see out my dodger like it is real glass....