The point is to see what muscles or part of a muscle is worked by doing a specific movement. For instance by doing a tricep pushdown with a straight bar works what part of your tris verses a rope. Maybe a bad example but you should see the purpose. That way you can target what you need to bring up and what movement works that area for you. No mention was made as to soreness equaling a good workout. This statement was strictly about how to target areas you want to work.