Most Tractors and some Implements have multiple holes to mount the 3 Point TopLink. Why do you need so many???
Well it all depends on the Implement and uses...if You need the Implement to Raise Level or in the case of longer implements and implements with PTO shaft you may require more kick-up of the back end of the implement to get through low areas or to prevent damage to the PTO Driveline.
The Higher the Hole on the Tractor you connect too the more level the implement will raise. As Can be seen in these images the Finish Mower Comes up more level to the ground. It can still be adjusted by the length of the top link to operate level when in the operating position but the Higher you mount on the tractor the more level it will raise throughout the lifting cycle.
The lower you mount on the tractor you will see that it kicks up the implement on the back end which make it go through low areas or creek crossings without hitting the ground. Also works good on PTO Implements to Keep the PTO Shaft from hitting the implement and damaging the PTO Driveline as the implement tilts forward. But can still adjust the length of the toplink to position implement at the correct operating level when lowered. As can be see in these images.