Selects Position Control for equipment working above the ground, sprayers, slashers etc. or Draft Control to control soil engaging equipment like ploughs and cultivators.
Position control means if the control lever is halfway up the quadrant, the lift arms will raise halfway up their travel.
In Draft control pressure on the top link controls the lift arm position depending on where the lever is in the quadrant. At the top end of the quadrant a little pressure on the top link will cause the lift arms to raise, lower down the quadrant more pressure will be needed to do the same.
You can try this yourself by putting a lever on the top link and pushing it.
Your picture shows the lever in Position Control.