/ic/ - Artwork/Critique

Can anyone offer advice on how to draw hard/soft edged shadows quickly? Right now I have one shadow layer than I'm brushing on and erasing away from, but in order to get really soft edges, I need a large brush that often overlaps other finished edges. Is the only solution to use tons of temp layers? I often see people painting on just a few layers and I don't want to use a million layers if there is a better way.