Soft Alt
With the introduction of RVSM airspace, 'soft' altitude has mostly been replaced with 'soft' or 'lazy' autothrottle speed control, for obvious reasons. Both modes are essentially for saving fuel, and they do. Keeping the engines 'purring' at a constant speed is much better than having them 'hunting' to maintain a set airspeed/Mach number. 'Soft' altitude would allow the aircraft a certain 'lattitude' in pitch to either speed up or slow down without the engines having to do the same. It was removed in RVSM aircraft and now the aircraft is allowed to speed up and slow down but not climb or decend.
Rgs.
Bob.