What is the reason for the grounding screw on some of the newer, premium light switches? Is it always necessary to bond the switch to ground, assuming the rest of your fixture / circuit is grounded?
Because you can put a metal face plate on it and the grounded metal strap is what bonds that plate to ground. Even when using a plastic plate, the metal screws are still exposed and need to be bonded. If the yoke were plastic, then there would be no need to ground them.