Energy consumption is related to the production of pollution in one form or another, so even in times when energy is plentiful and cheap, energy savings can't be left out of the discussion.
Platooning vehicles produces a significant reduction in energy use, because of reduced aerodynamic drag. Compare the two graphs below for vehicles in the U.S. EPA economy cycle.  The first is for a small single electric vehicle, the second for 20 such vehicles in a train behind a (much larger) engine
This is not the best showcase, because the speeds are relatively low, but even here around 30% less energy is used per car--and that includes energy used by the Engine. 
Combined with the ability of the Engine to absorb the large energy spike from regenerative braking, FlexiTrains are extremely economical to run.