I also went through the specification 29.274, "Bearer TFT" is an optional IE in create session request and create session response messages because default bearer can be used to pass internet APN data and if there is no restriction on type of data to be flown though LTE network there would not be any need of packet filters.
In case operator want to put restriction on type of packets to be flown through network and wants to charge differently for each different kind of data, network creates and apply different packet filters.
Dedicated bearers are created when a particular type of data can not be passed through default bearer and QoS requirement for the packets is different. When downlink packets arrive at PGW, SDFs are evaluated against the IP packet and mapped to relevant TFT. In this case it make sense to apply TFT filters because at least two bearers (default and dedicated) would be present and network has to choose either one of them.
I don't have working experience in this area so I am not sure on my understanding.
