This is a good drill to use when learning to keep the spine angle through impact. This allows you to be hitting balls and feeling the right side fire through the impact area.
Start off by hitting softer shots or pitches before moving up onto full shots. The idea with this drill is to learn to move the body more efficiently through impact, not to hit perfect shots.
After a short while you should be able to hit nice crisp iron shots to the target.
When you get to this stage it can be a good idea to hit 4 balls with the right foot back as shown, 3 balls with the right foot slightly back but not as far and followed by 2 balls in normal set up.
Repeat this over and over remembering to FEEL the same sensations as you are getting with the foot pulled back.
Have someone check that you are doing as intended or video yourself to make sure your practice is effective.
Get more videos here: http://wefixanyswing.com/videos/
Filmed at Troon.