Use cases:
Taxi-web-apps, transport-web-apps or web apps for other branches of business. Sites where the user may want to "broadcast" his/her location to.
backgroundTracker4WebApps also makes it possible to "hide" yourself on all the sites with a single button click, as well as "showing" yourself when you are ready for that.
Here is a list of controllable sites: https://gavott.com/backgroundTracker4WebApps_ListOfValidSites