It's sole purpose seems to be as the "come alive" button when you select "Turn on With Power Button Only" on the config screen. The only way to shut it off is by setting the preferred "stay on" interval also on the config screen. However, the firmware is so shaky that that only works half the time. I have mine set to .5 minutes when connected or disconnected from AC and I often have come home at the end of a day to see the display on, connected or not. Sometimes it goes off, sometimes it doesn't, sometimes it just comes on by itself.

Dave.