I know everybody, including me, uses the line with the least stretch for all control lines. I can see this on the jib because a little change in sheet tension makes a big change in sail shape. And it's the wrong way, the sail gets fuller as the sheet is eased (or stretches).

But on a mainsheet if you get a big gust it's not a bad thing to ease, very slightly, and then sheet back in again. It's like the energy was stored briefly and then given back. Would more stretch in a mainsheet be a good thing? Discuss.