Weird. I disable Bluetooth on my iMac. Don't need it. Lately the kids session (managed user) was running very slowly. Bluetooth (blued process) was sucking resources. Turns out it was enabled in that session, even though that user can't alter network prefs. The menubar icon showed bluetooth was on. I disabled it.
Session is now useable, but still a bit sluggish. Odd. I suspect a glitch; I don't think Apple thoroughly tested how things work with a limited-privilege user.