Tim,
The other purpose of this breathing is that it is very stimulating to the internal organs and lymphatic system. By drawing your breath in and out in the ways instructed you are both drawing and pushing Chi into the organ systems thereby building their strength.
Increasing organ strength is paramount as it will affect our ability to digest, assimilate, build and strengthen. The breathing is counter intuitive if you're used to traditional breathing for singing, speaking etc. That's because it's purpose is different.
Hope this helps,
Peace,
Peter
