I have some thoughts over this query and would like to share here.
In rural areas, network nodes density may be less. I meant to say, no. of nodes in the network would be less so the event based TAU would be helpful.
But in case of urban areas where the no. of network nodes (macro cells, pico cells and femto cells) would be more and assume a single tracking area covers all these cells . In such case, an operator would prefer to have periodic tracking area update procedure for an UE.
Timer 3412 is defined for the TAU periodic timer. The default value of TAU timer is 54 mins.