This is not the engineering of the sail, just my experience with it.

When I put the squaretop on the Tiger I expected to get better performance out of it in light winds. The first day racing it was miserable. I was sailing in bumpy conditions in light winds and finished at the back of the fleet. The next morning I looked at the leech, while on the beach. I noticed, sheeting and loosening the main, that there was a huge hook at the top while sheeted in. I marked the mainsheet where the hook stopped and raced that day with that slack in the sheet. I finish in the top three with the same conditions as the day before...much better.

So where do I think the squaretop shines? In windy conditions where you do not want to do too much sawing if you hold your own mainsheet. As Rick pointed out the top of the sail will depower on its own as a puff hits it. I usually play my own mainsheet and do not like to pump it in and out. Doing that too much, one handed, hurts the shoulder. The squaretop is perfect for this application.

Later,
Dan