Eric, basically position control will let you do what you are saying. Draft control is something else entirely. Personally, I don't know of any use for it except for pulling implements that are into the ground; i.e., plows and such. If the plow is pulling easily, then it can go deeper into the ground, and if you come to a place that it's pulling too hard, it will raise to a shallower depth until the going gets easy again, and will then go back down deeper.
Over simplification perhaps, but that's the basics as it was explained to me by a farmer who used it (I've never used it personally). It keeps you from bogging down if the going gets too hard. /forums/images/graemlins/wink.gif