If  Advanced Config -> Update Schedule -> Locate device on check-in option has been enabled,  device location will be updated to the server every time a device check in [whether the check-in is asynchronously requested from the server side, or initiated automatically from the device agent according to preset check-in schedule(s)].   

With data collection rule, location data is recorded by the device agent at REGULAR interval (shortest is every 2-minute) whether the device is online or offline, and the buffered data will be flushed & synced back to the server for location/track display in the device's location tab in the web-console, alert policy (e.g. geofence entry/exit), and other location related tasks.   

If neither of the above are used, device location will only be captured by the device agent and reported back to the server when the "locate" device action is requested via the location tab of the associated device  in the web-console while it is on-line.

The data-collection rule approach allows the most complete set of location data to be collected and stored in the MobiControl database for subsequent processing/display, but is also likely to be the most battery power hungry.