Every grinder manual I've seen (yeah, I read the papers that come with even the most basic of tools) cautions against turning the power on and off rapidly, particularly if the wheel hasn't come to a stop yet. I guess it could eventually loosen the grinder wheel. I don't know if that's actually true or not, but I try to abide by it.
Found the PDF of my manual - here's what mine says, at least:
DO NOT TURN THE MOTOR SWITCH ON AND
OFF RAPIDLY. This could cause the wheel to
loosen and create a hazard. Should this ever
occur, stand clear and allow the wheel to come to
a complete stop. Disconnect your grinder from the
power supply and retighten the wheel nut securely.
Last edited by Jessica Pierce-LaRose; 01-25-2013 at 9:47 AM.
" Be willing to make mistakes in your basements, garages, apartments and palaces. I have made many. Your first attempts may be poor. They will not be futile. " - M.S. Bickford, Mouldings In Practice