Important Things - The lower body

Here are my 2 cents' worth, higher level players might think differently.

Yes, it is important if you want powerful loops and smashes. However, it is not always possible to do it when the ball is coming in too fast or you are out of position. Waist is the most powerful but slowest to setup and slowest to get back to ready, arm is less powerful but faster, wrist is even less but you can react almost instantly. Transferring weight from the right (back) foot to the left (front) foot helps you twist your waist faster hence more powerful. The pros have much stronger arms than average players so in some situations their shots look fast and spinny even without using the waist. Once I saw a picture of Wang Hao with what looks like a 40 lb weight on his elbow and his arm is still 90 degrees to his body. However, given the chance I don't see pros using less waist and weight transfer than any regular players. For example, the most powerful smash I can think of is the smash against a lob/high ball. With ample time to set up the smash and less worry about a fast return the weight transfer is to the extreme where your right (back) foot actually lift off.   

Personally, I will try to go to the ball and only reach if I know I have absolutely no chance of getting to it in time. Whenever I'm reaching for the ball I produce a weak return. More often than not, my opponent will give me more until he wins the point. When I'm in position I will try to pin him down at the other corner, worst for worst I can still be in a rally of equal terms with him. By the way, most people will tell you you shouldn't change strategy just because it is a match point.