cchoate,
I'll try to describe position control in layman's terms...
Without position control, the 3-point lift mechanism has "UP" and "DOWN" control of the lift arms which allows the operator to position 3-point equipment at whatever point the lift mechanism lever is released (full up, full down, or anywhere in-between). Once you depart from a known setting (a desired mowing height, for example) you may have trouble finding that exact height again. Additionally, it is possibly that the 3-point equipment may creep down from an desired setting.
With position control, the lift mechanism arm has a range of numbers (say 1 to 8) that represents full up, full down, and intermediate positions. Once you depart from a know setting (setting 4, for example), you can return to that same setting and the lift mechanism will keep it there for you.
Now when it comes to the next feature, DRAFT control, I'd have to refer you to a post on this board about 2 or 3 years ago that had an excellent description of both draft and position control. I have a copy somewhere...
Kelvin