Hi everyone who responded to my post. I know the Russian regimens principle of a dropped wrist seems too simple to be valid and I certainly do not endorse a one size fits all approach to piano technique.I will try to explain...
Years ago, when I was a tertiary student, I was lucky to learn for a short time from a Russian concert pianist - Igor Hmelnitsky. He taught me to practise slowly with very active finger work, with the fingertips slightly above the key surface, and with a firm, but not forced, follow- through of the finger stroke to the keybed in the Revolutionary Étude and pieces of similar difficulty. In addition, he advocated a downbeat on every 2nd semi quaver, then every 4th semi quaver in Étude Op 10, No 12 at a moderate speed. As the tempo is increased, he pulsed in this way with a tension-free wrist on every 8th note - the idea being to think in larger mental groups and pulse less often as the music's tempo increased. He didn't, however, advocate dropping the wrist during this pulsing to its extreme range whereas the Russian regimen does so IN PRACTICE ONLY. This extreme movement becomes a mere "give" at the wrist when performing the finished piece.
Also, this wrist dropping doesn't determine stool height which can be adjusted to suit the individual and the piece he or she is playing if you wish. I personally sit with my forearm at least level with the keys (parallel to the floor) and begin my students this way. Any lower would result in poor hand posture and lazy finger action in my beginning students and for myself would not provide that sense of space to descend into with the arm and hand during the "pulsing" on significant beat notes in the piece.
Because my technique was above average, but never completely assured, especially when playing virtuosic repertoire, I have studied many technical approaches over time including the Taubman approach from which I have always gained valuable insights. Dropping the wrist more fully, however, has unlocked a whole new dimension for my technique in all repertoire at speed, especially the Chopin Etudes and Op 10, No 1 in particular.
I am talking physical freedom and facility at speed only here. There are many other subtleties to piano playing besides the pure physical mechanics.....for other posts maybe if I can offer something relevant and helpful.