THose that use the stance do so for various reasons. I have been investigating the usefulness of the stance myself. I can honestly say that currently I can't say that it has befitted me and that I am any more stable in it.
With that said, I don't blame the stance, but my execution of it. I have felt many people that are in the stance and they are very comfortable and stable. The stance it self may not be a fighting stance, depending on your view point, but it defiantly trains the knees if done correctly. That carries over into the other stances like Bik Ma. I think of the stance much like how some people might hold a pencil at the base when writing. It gives stability and flexibility, at least once you are sufficiently able to do it correctly.
The knees and elbows are linked together and play off of each other, atleast in some people wing chun. And the knees need to be inwards to create a certain effect.
One point I would like to make is that if there is pain in the knees caused from any twisting, your doing the stance wrong. You need to be very carefull that your not causing the knee to twist improperly. The knee is a hinged joint and is designed to bend in one direction. Any pain you feel should just be in the muscles and not the joint. Few people have tried the stance and put the wrong pinching or pressing inwards direction which torqued the knees incorrectly. Many of them reported knee problems. I have sensitive knees as do several others I know and they don't report any issues with the stance. In fact, several others have actually noticed stronger and SLIGHTLY healthier knees than before.
That was my long answer. The short answer, I think it is to link the knees and elbows.
I've only just discovered my error, and I'm going to have to replay whole sections of my life through my mind to see what confusions I may have caused or fallen foul of.
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