I was criticized once (by an "expert") for not tumbling my brass. Something about dirty brass potentially hurting the resizing die.

My pistol brass needs no lube, so no need to clean it afterwards. I use Lee sizing lube on rifle brass, and it cleans off with a simple wipe, so no need to post tumble.

I don't know if its harmful, but I never saw the need to do it anyway, so why bother worrying about it.