By forcing a/c to leave a level earlier than they want, I understand that the initial rate of descent won't be that high. However, at least they are going down. Being told to leave early means that normally something is in the way, or the one in front is descending and we want you in similar levels to speed effectively. Expediting an a/c already in the descent gives a more immediate resolution than one told 'start descent now, expedite' due to the delay in initial downward movement. In the ideal world, (like the sims) getting an a/c to leave and giving the restriction, I would like to see the rate of descent adjusted to give a constant rate of descent to hit the restriction, but I know in the real world this'll never happen.
I've started on a couple of my sectors now to give intermediate restrictions to ensure that an a/c is at the level I want it to be at to able separation in the awkward corners. It works well and creates none of the problems in this thread.