I've only ever used ccleaner for its registry cleaner, and only when I wanted it to clean something like an incomplete uninstall that I suspected was causing a problem. Never had it run "in the background" for anything.
I've never had it running all the time either but realised it WAS doing so after the last Ccleaner update - and went to disable it. But got a dire "warning" when I did. So I came here for the darn good advice I knew I would get !!