If I am grinding a full hollow I do everything on the rest apart from when I blend the belly into both the grinds when I will use a small wheel and a mix of non-woven and trizact belts freehand.
All my wedge blades which is what I predominantly grind, are done freehand, apart from something like a 20th century American style wedge (think Union spike) which I grind on the rest also. I find you want more than freehand accuracy if you are grinding a razor with a straight edge whereas something like a 19th century Sheffield style wedge with a slight smile you have a bit more margin for error.