What happens if when installing a light fixture you don't use the ground wire?

The ground wire is to ground a metal object so if a hot wire touches that object it will kick the breaker and break the circuit hopefully. If not grounded to the metal light or metal box for outlet,switch.etc. and If for some reasons the Hot wire was touching that object it could energize the metal object and also YOU when you touched it. Under the right conditions it could kill you because of metal object not grounded properly