A simple beacon-based proximity system can just detect the presence of a beacon and trigger some actions based on seeing it. Another interesting use case is to build a positioning system, where our app would know the precise location of the device on which it is running.
It is very similar to Global Positioning System (GPS), a system of satellites that can provide the app with geographical coordinates where it is currently located. GPS is great, but it has its limitations. First of all, the accuracy of GPS is only up to a few meters. The second limitation is that it only works outdoors. With beacons it is possible to build much more precise systems, with location accuracy below one meter, and which work both outdoors and indoors. A good example of such a location tracking use case would be to find your way in the underground parking garage...