This button is used to "wake up" the IP Phone Display from Sleep mode (power saving). So if you have it set to sleep until 8:00AM on weekdays and you arrive at 7:00AM the display will be dark. Use this button to bring the display up :)
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.