To add another controllers point of view, I have worked in Toronto ACC, Geneva ACC and now Bahrain ACC. I have used rates in all 3 places. Moreso in Geneva because of airspace contraints. You ask.. why are we stuck low then given climb to be level in 4 mins? Or why are we given a rate all the way up. There are many reasons, some are airspace restrictions, some are due traffic and others are due to the controller not wanting to get burned. I have been burned way too many times giving a descent and especially a climb.."XXX climb to FL 340 and reach by..." Aircraft being too low, or on a descent aircraft being too high. Yes some pilot might view this as "US" flying the plane but this is not so.. This is ATC providing separation and adhearing to agreements with other control facilities. In periods of light traffic I would normally give descend to.. and reach by XXX. When I am busy, I use rates all the time. It also shortens the number of transmissions.... How many times have I seen this : I ask an aircraft to start the descent. I am asking for a reason, then the pilot is giving me a couple hundred feet per minute.. It happens ALL the time.. So if i ask for descent, I am ALWAYS going to give you the rate if I am busy. Someone on this site suggested that rates are more of a procedural thing? ... A busy radar environment, you cannot do without.. unless of course you want to be non stop talking ...transmitting to the same aircraft 4 times