These networks were originally developed for bursty data. People are now interested in also using these networks for isochronous traffic such as voice, audio, and video. Network throughput is determined by congestion.
Congestion is determined by topology and statistical blocking.
Some network topologies are blocking. One path blocks one or more other paths. This blocking multiplies the effect of the traffic. As an example, two paths through an 8 port Butterfly or Banyan network can be shown to block the other 6 paths. This results in an effective factor of three increase in the traffic.