This app is showing an azimuth line on the map for a given location and angle. Sometimes in strong electromagnetic field and close to the metal things, compasses can't work properly. In those kind of situations this app could be useful to find reference points on map and help to correct align the antenna.
It should be helpful for professionals who mount sector antennas (f.e. GSM sector antennas) or amateurs for self-installation of GSM repeaters or dish antennas.