My reading is that Ac will be issued a "fixed" IAS to fly... maybe our company's interpretation of the "rule"?
Problem today was, even before LTMA, we were asked to slow "Min Clean". Fine - we did, and planned descent on that basis (~200KIAS). Then in descent asked to go to 250K, then 280K level
And then a different LHR STAR (BIG v LAM), and finally held for 10+ mins.
The acceleration to a low altitude 280K, level segment cost us a lot of fuel, especially when combined with an early descent, and a need to hold anyway.
So if you want some feedback, then being given a (fixed?) IAS to fly, prior ToD, great... it can save fuel / holding etc.
But, to later increase that gets costly, and if you can, a "rule of thumb" of never
requiring a subsequent increase in that IAS will be helpful in fuel terms. An "offer" of an increase might be fine, and may be accepted on occasion
NoD