I can't sail without them. My first spin did not have them. When it came time to replace it, the new sail had them, and my down wind improved dramatically. Immediately rumors began to circulate that I was cheating. People "new for a fact" my spinnaker was over sized. In fact it measured slightly under sized.

That's the difference tell tales make.

I'm scheduled to sail Wednesday, I'll try to remember to get measurements and some photos.