I also have that question: what is the purpose of mast pins?

They make sense on boats which have a hole drilled directly through the ball mount (some Hobies) - in that case, the pin allows the mast to be raised in a straight line without veering to the left or right. Then it can be removed when we want to the mast to rotate (i.e. when sailing). When the mast is small or light enough to put that kind of weight on a pin, this makes a lot of sense.

But on my Nacra, the pin only seems to hold the mast to the ball bearing, without controlling direction. Unfortunately this doesn't do any good whatsoever. One time we dropped the mast while raising it; the force was so great that it removed the mast from the ball and shattered the pin! (amazingly, the mast and the ball were both unharmed).

The lesson seems to be that you're "on your own" when it comes to raising the mast, and nothing is a substitute for manpower and a good winch.