down wind sailing

I'm curious how much weather optimization plays a role in performance. Guessing I'm not the only one obsessively checking the weather before heading out! What do your ideal conditions look like? I'm still trying to figure mine out. I started working on an idea to link sailing & weather insight...

I know I've seen it but can't find it. So need to ask. In very light wind how do I keep my sail out going down wind? I thought there was a way using bungee cords. Maybe using the sheet somehow? or the halyard? A description would be great, even better a link to pics or video.