I noticed increased wear on my belay loop from rapping.
When I rap, I "walk" down the wall, which causes the leg loop to saw back and forth across the belay loop. If you rap with the device on the belay loop, that probably isn't an issue, since the belay loop is free to rotate around and distribute the wear.
But I kept a sling girth hitched to the belay loop and used it to extend the belay. That kept the belay loop stationary and the leg loop wore on the same spot every rap. I suspect that after some time it would have seriously damaged the belay loop.
Once I noticed it, I started removing the girth hitched sling and girth hitching it each time, which should distribute the wear. I think I'll start putting a backup sling through the leg and waist loops as well.