Unless you hook the ground cable to the alternator I can not imagine anything happening, another "old husbands tale".
I do know that with late model computer controled cars, you should always disconnect the battery. But honestly, it is a CYA deal, I have NEVER seen any kind of damage what so ever concerning this.
I have however seen exactly what Oldred is talking about. I have seen hinge pins welded because the guy gounded the body and welded on the door. I have seen a throttle cable burn right in half because he grounded the exhaust and welded on the body! Put your ground as close as you can to the weld and ON THE SAME PART.