Thanks for the replies. The reason I asked was that Ulman told me they put them on their spinnaker. They said the sails are so flat they are helpful.

Another question…

I have read wouter say that he would rather capsize than blow the spinnaker many times. Why is this? We got in a debate on the water about it and ended up testing it by flying a hull pretty high and releasing the sheet. The boat calmed down.