The Priority column on the Group Assignment Rules page shows the order in which group assignment rules are applied.
In the example below, consider an endpoint that is tagged "Seattle" and has an IP address that belongs to the 192.168.0.0/24 subnet. The endpoint is applicable for two rules. In this case, the endpoint is placed in the West Coast/Seattle group, since the Seattle rule has a higher priority level than the 192.168.0.0/24 subnet rule. However, if the Seattle rule is disabled, the endpoint is placed in the HQ group, as per the 192.168.0.0/24 subnet rule.