This policy setting allows you to display a custom message to users in the notification balloon when a device installation ...

This policy setting allows you to display a custom message to users in the notification balloon when a device installation is attempted and a policy setting prevents the installation.
      
If you enable this policy setting, Windows displays the text you type in the Detail Text box when a policy setting prevents device installation.
      
If you disable or do not configure this policy setting, Windows displays a default message when a policy setting prevents device installation.