Ground wires are intended to carry current only when there is a failure in the electrical system that would give the current a path through your body.
Given that ground wires are a protection against failures and not part of the operation of switches or other equipment, you should not have any second thoughts about connecting ground anywhere.
If your switch has a screw to connect a ground wire, use it (unless you know for a fact that the ground will be picked up by the connection to the metal box). If it has a factory-attached ground wire, definitely use it.