At my lower skill level, I would not have wanted to wear boot covers or over-the-boot tights for practice because I usually felt the need to adjust the tightness of my laces at least once or twice during a practice. They were never tight enough at the beginning until I'd done some warmup stroking and the boots themselves softened up a bit.
Yes - but the type of inexpensive (e.g., thin lycra) boot cover I used to use (before my boots broke down so much I really don't care anymore) can be pulled out of the way in a second or to, and put back in place almost as fast. I also found that they helped prevent laces from untying.
The slick boot cover did make it a little easier to glide on lunges... Plus, I had an ice dance instructor who insisted I get low enough and on deep enough edges that the top of my boot on the underpushing foot would brush the ice during crossovers and progressives. So I could glide a little better on those moves with the cover in place. (That was very hard on the boots for a different reason - deep edges, and the little amount of sideways ankle bend I needed to do that put a lot of stress on the boots. No boot cover could fix that.) Anyway, I'm no longer strong enough to stay that low.
For a while, when I skated in a very cold rink, using low level thin boots, I used thicker urethane boot covers that provided thermal insulation. I had to be careful not to trip over the covers; They limited how "neat" (i.e., close) my feet could come.
But like I said, boot covers are basically cosmetic. Little scratches and scuffs don't really matter to skating. And I doubt that in most cases they significantly affect the lifetime of the boots. The other stresses on the boot likely cause breakdown before the surface scratches and scuffs could develop into something structurally important.
Some people, if they want to hide scratches, cover their boots in tape (neatly wrapped), or repolish their boots (a bit complicated, because many boots have a clear coat layer on top that polish may not adhere to).
But if you like boot covers, and they make you happy, go for it! The weight is insignificant, and they aren't very expensive. Unless you have reason to think a skating judge would mark you down for wearing them.
If you do like the idea of painting your boots for a costume, it would be easier to get rid of the paint job when you are done if you instead paint a cheap disposable cover...