A task boundary is a template that allows the distribution of tasks in a cluster of cooperating nodes. Task boundary templates do not themselves perform any transformation, but they know how to transport the content from their input over the network to their output. As such they reside both on the beginning and end of a demux/mux pipeline that needs to be distributed over the network and run in a cluster.
This means that when using such task boundary templates, there should be one right after the demux item in the pipeline and one right before the mux item in the pipeline. The pipeline in between will be effectively run on the cluster, thereby releasing CPU cycles from the host machine where the rest of the transformation takes place.