As mentioned above, it's to increase the mental focus. I think in his book or video, he cites a study by law enforcement officers on the pistol range improving their scores by bending at the knees.
As Terry mentions above, if it doesn't work for you, you don't need to try and incorporate into your shot. Everyone shoots differently and just like the old saying in the restaurant industry about there's no such thing as an original recipe, so is it for shooting style and method. Garner tidbits from everywhere and try them, if it helps, keep it, if not discard it and move on.
I'd consider consistent hand placement on the bow, consistent draw length, consistent anchor and release as the gospel items. Beyond that, it's up to you to play around with what works for you.