From an approach controller perspective:
1. I'll apply a speed restriction IF and only IF I need you to fly at that speed for separation purposes.
2. I may lift a speed restriction imposed by a previous sector because I don't need you to fly at 220kts, you can fly at whatever speed you like (is most economical)
3. I need to SEPARATE you from other traffic, so when you do SLOW down, TELL me (my predict vectors only work when I have them switched on)
4. If I tell you to descend, then DESCEND, don't hang about, if I want you to take your time I'll say WHEN READY
5. If I ask you to keep high speed, let me know if you can't (My thanks to all ATP pilots out there who fly into EGPF who do 230kts to 4dme when asked)
6. Come and see how it works at our side, we can all learn from each others experiences)
7. Do any of you know the legal speed limit for class E airspace?
8. Bring back FAM FLIGHTS
Finally I AM the final arbiter about what happens in the airspace I CONTROL, the captain is the final arbiter regarding the SAFETY of his aircraft. I would certainly hope that if a pilot thought that an instruction I had given was unsafe then (s)he would question it.
We all have ine aim, that is to get the a/c and pax to destination as safely as possible.
We operate on thre principles:
Safe, Orderly and Expeditious
In that ORDER.