Sadly I have seen the result of what damage a cut off disc on a guard-less grinder can do. One of the guys in the hot rod club I was in was lying on his back with his head up under the dash of his '57 Chevy trying to cut something when the whole situation turned nasty. The result was the disc and machine slicing down his cheek and neck just missing his eye and deep enough to see the bone structure. Luckily, no major blood vessels hit and we have an amazing air ambulance system here in NZ. But he is not the handsome young man he use to be and has the scares to tell the story.