I do it because I like clean primer pockets. You also don't get any moisture trapped in the primer pocket which can be an issue if you try and reload the brass before the primer pocket dries out. Ask me how I know...
I do tumbling in water with ceramic media, dish soap and a little Lemi Shine. Tumble for about 2-3 hours. Dry brass in the oven for 30 min at 200 degrees.
The first indication a bad guy should have that I'm dangerous is when his
disembodied soul is looking down at his own corpse wondering what happened.