In the opening keynote presentation at the 2010 International Association of Structural Integrator's Symposium, Michael Salveson noted that the body works best when joints are in their neutral position, that is when all forces on the joint are equal. In this video, you can see people demonstrating undulations where they are exploring the movement of their spinal joints and helping create more balanced, neutral positioning and range of motion.
Michael also noted that in the Daoist traditions (Chinese medical arts), the joins is a resevoir of chi (energy). When a joint is weak or injured, it borrows chi (energy) from nearby joints.
The spine has 125 joints. As the central pillar of the body, its range of motion (or lack thereof) determines the ease with which a person can move. Try some of these undulations to create more chi in your spine.