I'm not sure exactly if that's how most pro coaches teach it! Certainly those that have been RPT trained do! I picked up on it when doing some work with Luis Mediero and Emilio a few years back. In terms of generating power on volleys it's really important to get these combinations right as they stop you having to/trying to do too much with the arm and allow you to control the body movement for maximum effect.
I may be average... but my average is still ****ing awesome