There can be two reason for the location reporting procedure which was introduced in Release 9 -
1. Location Based charging: PGW/GGSN needs to know the exact location of UE to have Location Based Charging.
2. Lawful Intercept: PGW/GGSN needs the exact UE location to enable LI.
When MME/PGW supports location reporting then MME will ask eNB to report UE location and when UE moves from one TAI to other TAI or from one cell to another cell, eNodeB will send Location Update message to MME. Which passes this information to PGW/SSGN over ULI IE (User Location Information).