It's not like an oil paint on canvas that no one ever touches is in any dire danger. So no, we don't really do anything to protect it. I suppose a big earthquake might smash stuff up but at that point the art would be the least of our concern.
We have a big geometric cut glass piece that is embedded on a piece of half inch lumber. If it ever crashes down I hope no one is standing under it, I worry about the floor. It's super heavy and mounted into the wall studs. I love it enough that I was willing to deal with it's weight. I don't think it's practically protectable but it might be in less peril than that which is under it.
There is a small painting on a wood substrate that has some kind if shiny shellac over it. Your question makes me wonder if it should be framed because I could see it getting chipped if it fell but I think a frame might detract from the piece, I'm pretty sure the artist intended it to be displayed without a frame.