hi to all and season's greetings
IMHE most radar controllers in the region i fly in..europe,north africa and the middle east will either instruct you to expedite r/d out of a certain level/altitude or instruct you to maintain a specific r/d for flow control especially in busy european airports,e.g frankfurt,amsterdam,heathrow
now changing cruise level enroute, a minimum of 500fpm is generally expected..i stand to be corrected by the experts