SC - The big difference between shutting down engines during taxi and saving on the APU is that there is no negative affect whatsoever from shutting down an engine, everything still works as advertised.
Wrong! Prove it.
Sorry R Knee and your point is???
Many 2 engine airplanes taxi in on one engine and 4 engine airplanes on 3.
All works well. Plenty of redundancy in the systems. Standard procedures for saving fuel.
APU restrictions on the ground are usually environmental. IF the ground facilities are good then ground air and ground electrics will be used where possible.