This option is extremely important, it defines the priority of one Content Group over the others and it is used to define what version of your website should be loaded in case someone qualifies for more than Content Group. Your default Content Group should have the lowest priority (e.g. if there are 4 Content Groups, it should have a priority number 4).
Whenever you set a priority to a Content Group, all other Content Groups will be automatically re-arranged to the next available number of priority for your convenience, for example: You currently have 4 Content Groups, you create a 5th group and give it a priority of number 2; whatever group had that number of priority will automatically be re-arranged to priority 3, so on and so forth, in this example, only the Content Group that has priority 1 would remain unmodified.
This is how it would work:
Let’s say you have 2 Contet Groups:
Content Group 1 is for mobile users coming from the United States.
Content Group 2 is for all users in general coming from the United Sates.
Someone who qualifies for Content Group 1 also qualifies for Content Group 2 so you need to assign a higher priority to Content Group 1 to make sure that mobile device users coming from the United Sates see the version of your website that has been assigned to them, and not the version of your website for Content Group 2 which is for United States visitors in general.
Note: Priority is NOT the name of a Content Group, a content group that is named Content Group 1 doesn’t necessarily has the priority 1. The names are simply the order in which they where created.