If you have two or more different sessions, from different sources (Armbeep device, mobile app, other devices,...) and you would like to have them as one session, you can merge them. 

Example: When you track a player on a match or practice with Armbeep device and mobile app, you will get two sessions (one from Armbeep device and one from mobile app). The best way to compare the data from those two sessions, is to merge them. The system will create a new (merged) session (group).