Proper Earthing is a must for safe usage of electricity. Earthing ensures a proper discharge path for the flow of electricity and hence is recommended for any plug pin connected to the circuit board.
It is always safe to connect the Earthing wire dug into the ground. All the grounding paths should be accessible. This path resistance from the farthest barrier to this grounding electrode should not exceed one ohm. One-ohm resistance or below One-ohm is the suggested value of resistance for an earthing path to be safe and secure.