Difference between Primary and Secondary monitoring locations
Primary Location is the main location from which your configured monitors will be polled according to your set poll interval. If a website is reported down when polled from a primary location, then the Site24x7 servers will check the status of the monitor from the Secondary Location and notify in case of downtime.
For instance, when a website is down at, say L1 (Primary Location), Site24x7 will check from L2 and L3 (Secondary location) as configured by the user and send notification only when the website is detected down at both the locations.