</font><font color="blue" class="small">( Can't you lock the 3 pt down with the adustment under the seat? )</font> No.
You can lock the hydraulics so the 3 point won't LIFT hydraulically, but it is free-floating, NOT locked down, so if the item being pulled hangs up and the angle of pull is such that the 3 pt would be raised above the axle, that is what will happen. It is important to understand that the tractor can turn ITSELF OVER, if there is resistance applied above the rear axle. The gearing in a tractor is awesome....and when there is resistance above the axle so the wheels can't rotate forward, the tractor frame can rotate backwards...resulting in rear rollover.
This is far less likely when the point where the resisting force is applied is below the axle. We quit selling three point drawbars many, many years ago once I understood this. I know many people get away with using them often, but they truly are an accident waiting to happen.