Allegedly, on or about 22 May 2018, Ed Greshko sent:
FWIW, if you investigate a little I think you'd find that for every user that logs-in for a GUI session there will be about 9+ processes that are left running and remain running. It seems these processes are then reused on subsequent logins by the same uid. I suppose this may be done to speed-up subsequent logins.
I had wondered about that, but I'd find that usually when I log out, that all my processes eventually disappear. Virtually straight away.
Sometimes, things would loiter around, and they'd prevent you from logging back in. With things the login attempt would think you're still logged in, or the desktop would never finish drawing up because it was waiting for stalled files that never closed when you first logged out, or there'd be no sound because pulseaudio had wedged.