Yes Andy, the stem-shortening job should be done with a jig to hold the valve square to the grinding wheel. I think most serious mechanics do this properly with the right jig, rather than doing it by eye. However I think most people working at home on old engines to keep them going, may sometimes do it by eye. Remember you can check the squareness of the stem-end every few seconds of grinding just by dropping the valve back into the valve guide (part of the engine) and inspecting how it sits against the tappet. The engine is a very accurate squareness jig.
