FYI - In some situations you might have a metal cover plate over an
electrical switch and usually there are metal screws holding on a plastic
Sometimes there can be a stray wire touching the metal box, the metal on
the switch, or a metal cover plate. I suppose a switch could also
malfunction internally and cause the metal on the switch to become
If the metal box and the metal on the switch is grounded, then should a
stray wire touch either, or touch a metal cover plate, then the breaker
should trip turning off the electricity and preventing someone from being
shocked (Or re-direct the electricity to ground).
I've seen situations where someone was doing dishes in the kitchen, went to
turn on the garbage disposal, touched the metal screw, and was shocked.
(Person was OK in this situation, but wanted it fixed of course...)
Certainly safer is better but in the grand scheme of hazards, ungrounded switch
yokes are pretty far down the list.