We did a pin in class tonight and I'm not sure why one would ever use it. You could very easily kick the person who has you pinned, and that is precisely what I said to my partner when she had me pinned and asked me to try to get up. I was on my back with my shoulders firmly pinned to the floor. My partner laughed when I mentioned kicking and said "no,no you can't play that way for this exercise" and that I was just to try to lift my shoulders off the mat. You wouldn't ever use a pin like this would you? What was the point of it?
(I asked a higher rank if they do any kicking at all and they do use them for attacks and they do techniques to counter them, so kicking is part of the training.)
So is there a reason for a pin like this?