As posted, it may not be an issue with the size tractors you are looking at. Of the different attachments, the bottom plow (if like a moldboard plow) would be the one you listed that draft control affects. Position control would work for the others, I believe.
When plowing without draft control, and the plow starts to pull in hard ground, the tires begin to slip and dig in a bit, thus causing the plow to drop deeper and pull even harder. This will bog a tractor down pretty quick.
But with draft control, sensing that harder pull and/or slippage (or compression on the top link), the 3pt lifts the plow a bit to find the spot where it is easier to pull, thus automatically keeping max. depth and continuous pulling.
Really hard to control the plow depth manually with just the position control of the 3pt, but it can be done with some practical experience. When the going gets tough, then lift slightly to relieve the load and then slowly get the plow back down where the depth is where you want it.