It has been common practice of crews to use less than all engines to taxi depending on ramp weights. In certain situations, it may be necesasary to start both engines on on a two engine aircraft. Once out of the congested ramp area where minimal turns are required, an engine is shut down. This saves a considerable amount of fuel at congested airports such as ORD, JFK, LAX, IAH, etc. Once after landing and the engines have cooled sufficiently, usually three minutes, one engine would be shut down. Since the aircraft is of at lower weights, and if delays getting on the gate are experienced, less power is required to get it moving to the gate.

I don't want to say that dispatchers don't care about the least time, versus lease distance route, but further analysis by them could result in fuel savings as well, reviewing winds, ISA deviation, thunderstorms, congested routes, etc. Also accurate projections in SIDS and STARS to be flown to ensure more accurate fuel burns would be helpful too.