Setting the primary zone is useful if you use multizone layouts and have more than one on your screen's playlist.
The duration that a layout will play is determined by the primary zone. For example, if the primary zone in your layout is a slideshow with 3 images that each have a 10 second duration, then the layout will play for 30 seconds before advancing to the next layout.
The primary zone may be either a slideshow zone or a text zone. Set the primary zone from the details window.
All multizone layouts must have a slideshow zone or a text zone when using multiple layout in a playlist.