Well, what other interpretations of "optimum rate of descend" would
you have in mind?

Depends what one is trying to optimize. Money, turbulence, time
enroute, arrival time (to coincide with an open gate), dive currency,
there are many things that one can attempt to "optimize", though I'd
agree that ATC is not likely to think of them all.

Jose
--
You can choose whom to befriend, but you cannot choose whom to love.
for Email, make the obvious change in the address.