Even the most accurate guidance systems in the world aren't going to produce accurate rows when you start dealing with planters that are 40-90' wide and run 30' behind the tractor. This creates the need for some sort of assistance on the planter or making the tractor/hitch compensate for the planter in some situations.

I never thought that a planter would move downhill as much as they do. We farm flat land. Our hills here are what some users here might call gopher mounds. Last fall when using autosteer in the combine and trying to follow rows, we saw where the planter had run 2-4" downhill on hillsides. In that situation, a hitch would be more than able to make up for it.