The winch can be used to do many things, from pulling trucks during a transporter challenge or dragging wood to the goldmine. It can also be used to assist you in accessing areas of the game that are meant to be accessed by boat or helicopter. The winch will drag you up hills too steep to drive or walk, or even pull you along the bottom of the water areas, even if your vehicle has stalled. I have accessed every island by car using this technique. A side note... if you are facing up a steep hill in walking mode, try moving around until you fall, face straight up and open your parachute. Press forward and you can go up the hill using the chute. I found this by accident trying to access the island that has no lower access point to gain the final flag.