I don't buy the 'cost saving' line,
Years ago it was shown to me, via paper calculations, that descending at hi-Speed below FL100 does not save fuel or time; therefore is not more efficient. Hi-speed from TOD does save time, if you get it correct and ATC does not intervene. It can be very embarrassing if you 'plan/brief' a hi-speed descent from TOD with no buffer an ATC turn you in shorter. Up creek with no paddle and sweaty palms come to mind. Speed brake the whole way, gear out early, flaps out on limits and a dive in landing config. Do it once and never do it again. Was it really worth it? You could ask ATC for more distance; so they put you in sequence behind a heavy, instead of in front, and your 'more efficient descent' just went to the opposite.
Easiest way to save time & fuel is a shorter turn in with a CDA to 1000'. More relaxing for those down the back, and certainly for those up front.