No offense, but this is kind of a no brainer. Would you sharpen an electric chainsaw with it plugged in?
My old table saw had a dead spot in the motor. If you turned it on and it didn't start, turn it off, spin the blade and turn it back on. I knew it was there, but someone else came and used it and got a nick in their thumb because they didn't know. Now suppose you didn't unplug it, thought it was off and went to change the blade? Sounds like a big painful mess to me.
Christian