There's a sort of half-rotation that occurs in reaction to every pass, and that gets potential help men in better position. The newer-style defensive positioning allows the switch to be called earlier because there's increased confidence that the help man will actually get there in time. The earlier switch allows the now-free defender to get out to the open man sooner. But I'm sure I'm way oversimplifying things. Here's a link to an article that goes into it more, initially posted by kimdaddy35. Coach Voigt has his own videos up on youtube about it. It's widely used all over the place these days, so there are quite a few videos around.