Not terribly complicated I guess. Push a variable valve lever and it raises hydraulic then when the valve isn't pushed it goes back down. But you're right, for such a pinpoint usage you'd think it wouldn't be standard.
So if you wanted to smooth out some ripples with a box blade would it be better to use or not use draft control? Or just do multiple passes?
I've used draft dozens if not hundreds of hours. My Kubota and Ford both have it. I've never used anything but mechanical draft. It's very easy to describe.
Older tractors (60s 70s) versions usually only had one control lever. A separate lever flipped the system into/out of draft mode. Later models use 2 levers. Let's talk about that method.
So if I want to use draft I place the normal use 3pt lever in the lowest position. Now I control the 3pt with the draft lever. Let's say I'm pulling a 3pt moldboard plow.
I determine the maximum depth I want to plow. I set the stop adjustment on the draft lever at that position. So everytime I drop the plow with the draft lever to the preset stopper, my plow will always plow at that maximum depth. How does it do that???
The top link assembly on the tractor is not rigid. It's usually mounted using a very strong spring. Somtimes using a compression system with a durable rubber bushing or some type of system that compresses and extends by the push/pull forces applied by the top link on my plow. Clear as mud right?
So I drop the plow with the draft lever to the stopper and start forward movement. The plow immediately heads for China (digs itself into the ground. This causes extension forces on the top link. The plow wants to go deeper. As this force increases it begins to extend the top link assembly on the tractor. As the mechanism extends it begins to move the controller inside the tractor toward the position of raising the 3pt. When the force is great enough lifting action stops the descending plow at the depth you previously determined. If the plow for whatever reason starts elevating above your preferred depth the top link assembly compresses and lowers the 3pt arms.
This process repeats itself however often required to maintain desired depth. If I have my plow adjusted properly, i.e., sitting flat laterally and level front to back, these automatic adjustments are barely felt. I plow all day and my depth basically stays the same. Plow pulls easy. Tractor maintains speed and traction. Life is good.
There are other implements that might benefit from Draft Control but none as effectively as the Moldboard Plow.
Also understand, a tractor without draft control cannot control the 3pt action with the same precision and smoothness. Without Draft it's left up to the operator to make those adjustments. Simply not possible.
I'm not talking about plowing your garden. I'm talking about plowing acres and acres for hours and hours.