Thanks Brian! It's mainly to be able to observe the extraction in real time. By being able to watch it from start to finish, you can control things better and have a better idea of how the grind and tamp are affecting the outcome. As a result, I think being able to do this does improve your shots. The espresso is also in contact with less metal during the pull, so there is maybe slightly less influence due to contact with the metal of the portafilter/spout, etc.
After using it, I would never go back to the old method I don't think.