Master Wing Cheung demonstrates how to position the Kua (pelvis) when performing Chi Kung. This 7.08 clip also contains a demonstration of the 'difference of using your knees vs your Kua' (3.34).
It's a simple and effective technique to help protect your knees. I'm always conscious of the Kua whenever I practice my Tai Chi and Chi Kung.
And this awareness is important when practicing stationary postures that are held for a period of time.