Back in the day even when the price of fuel was not an issue, we would use max thrust for takeoff, max climb thrust to cruise, and monitor time of climb to next flight level. This helped to keep more fuel in the tanks to make destination with extra. We would stay high as long as possible, and basically glide from altitude to about 3 to four hundred feet AGL. High speed descents do not consume any extra fuel, provided you are at flight Idle from TOD to the same given point in space we are fully configured.
Larger aircraft may require greater flap setting for takeoff provided climb or obstacles are not an issue. This keeps the ground speed down during high gross weight high temperature days, thus keeping in line with the tire speed limits.
Bean counters or even actuaries that have true knowledge of commercial aviation need to run a cost analysis of fuel consumption versus to the cost of wear and tear.
Less than all engine taxi will save fuel, especially at the light weights after landing, and when a gate is not available will save fuel. This is of course the engine has had adequate time to cool down after landing. We do it all the time. However, the same may not apply during taxi out at high gross weights because of the additional break away thrust required to get the jet to move. Assembly line aircraft are not equipped with the sophisticated forensic type of instrumentation see true fuel flows or fuel consumed to the degree of accuracy to make such detailed fuel consumption analyses. More data, on an airport by airport basis, is needed to determine the fuel savings too. To name a few… fuel density, tire pressure, taxiway slope, aircraft gross weight, ambient pressure and temperature, cross wind components, will all may be minor by themselves, but combinations of all may have relevance.
Also, the manufacturer will indicate gross weight recommendations to be observed when performing less than all engine taxi in order to avoid fan blade flutter.
In an ideal operation, a tug to and from the terminal to the runway would save tons of fuel and money. Imagine the number tugs and labor, not to mention ATC communications and coordination required accomplishing this feat in say JFK or ORD, or even LHR would be high too. Would airport authorities want to design and construct special "TUG ROUTES" to help accomplish this means of fuel conservation and the added bonus of helping the local ecology?