In the storage yard where I keep my fiver you can tell the rigs that used to have covers because of the tie-died arcs scraped onto the sides. The wind shreds the cover and then the shreds flap and kill the finish.
Every time I see a new cover go up, I make a mental note and then check on them throughout the year. It never ends well.
There's usually collateral damage to the rigs on either side too. If either of my neighbors ever put on a cover I'd ask management to assign me to a different space.
So I agree with Grit that they're a regional thing. And in some regions they do more harm than good.