First, I would like to explain what is the need to tracking area procedure and it's possible uses.
LTE network has concept of cells and tracking area. A LTE operator managed it's network using cell Id and tracking areas. One tracking area may cover set of cells or sites. Usually, network operator doesn't like too large tracking area or even too small.
MME may ask UE to report periodically its tracking area. One point to note down here, by using tracking area update procedure, MME came to know about location of an UE at the cell level as well. Assume an UE attaches to the network using a cell which belong to Tracking area code -1 and other cell belong to the same eNodeB belongs to different Tracking area code -2. In that scenario, non-periodic TAU procedure would help to network by avoiding a lots of signalling since whenever UE moves from cell1 to cell 2, it executes TAU procedure.
Now assume, there are 10 eNodeB and all the cells belong to eNodeB having same tracking area . In that case, periodic-tracking area update would be beneficial. Whatever I have mentioned it's my personal thoughts/understanding of the LTE system.
I was realizing another reason that urban area' s may have smaller cell size (to support more capacity as per) and rural may be even large cell. Now consider a scenario, A LTE UE attaches to network in urban area and moving towards rural area, in that case, when UE reports its current location (cell in overlapping zone - urban to rural), MME stops periodic tracking area and informs to UE in TAU accept message. This is also my understanding.