Using the darkening tool available in many drawing program gives instant and easy shading, but it looks, awful, if just the slightest overdone and people also smudge their drawings too much. On paper it would be like taking a wet sponge and smear it all over your sketch, now that's cool and all but also messy!
As for editing, an eraser always work if you put down your original lines lightly on paper. It's of course true that you have great possibilities using a computer
. It will be interesting to see what you make.