I was thinking about this today. I use my top burner setting for boiling water in my teakettle. (Before I got my teakettle, I used the boost setting with a good small saucepan.) The only other time I use the top setting is when I preheat my CI grill pan. I preheat for several minutes and then lower the heat to 6.5. I use the second highest setting for my wok. The highest gets it too hot too fast for my comfort.
When do you use your highest setting? When do you boost?
And anyone ever use the lowest setting?