No feed-back control would be like the typical front-loader circuit. You open the valve to make it move, and close the valve to hold it in place. Repeatability is up to the operator to judge the position. Things like leak-down tend to make the positon slowly change with time.
Position control has an active valve that maintains the draft arms in a set position according to a control, often marked with arbitrary, but at least somewhat repeatible settings. It will automatically adjust the rockshaft to the set position and hold it there (gravity doing the holding in the down direction).
Position control is useful for things like grading with a blade or landscape rake where you want to have the blade at a set height in relation to the tractor wheels and you are trying to create a level or smooth surface.
Draft control has the feedback valve connected to the top link. It senses how hard the plow is pushing forward on the top link. The deeper the plow is digging, the more it trys to pivot the hitch forward, pushing forward on the top link. The control valve would then raise the plow a bit maintianing a constant force on the top link. If the force is too low, the control valve lowers the plow a bit, causing it to dig deeper and increase the force on the top link to the desired set-point.
Maintaining a constant plowing drag should correspond roughly with a constant plowing depth regardless of the lumpiness of the ground. So when your front wheels go in a little dip or over a lump, or the plow runs over a dip or a low spot, the lift arms get adjusted to maintain the same plowing drag force and thus the same plowing depth.
One is not "better" than the other, but If you are serious about plowing, you will want Draft control. Most CUT's are not used for serious plowingg and for most of their comon uses, Position Control is what you probably want.
- Rick