Had one time someone shut it off because the ball got stuck on the inlane switch. ( a very slight nudge knocked it loose).
Then I had another time someone turned a machine off because the playfield was smoking so... Turned out a switch got stuck closed and burned up a coil and transistor. Based on those two extremes, I'd say turn it off when in doubt.
I put a message box up one time, half the time you get dick drawings or stuff that is completely unrelated.
Have my phone number on the pinside map, but not on my machines. Always been a little hesitant to do so, figure I have enough regulars so that give me the run down.