I need help to understand null groups for rigging purposes

Hey! I am following the book "Body Language Advanced 3d Character Rigging" and it talks about null groups in this one part. It explains how to get a null group clean but doesn't really go in depth about types of problems that can arise. It says that all controls should have a null group to prevent some future errors in rotational or translational values when animating which I understand. The problem is, it talks about doing a parent constraint on the null group to the control itself (the control is moved beneath the null group before constraint). When I do it, I get double transforms happening along with other undesired results. There are no previous values in the Translate, rotate, or scale values before hand. All the joints are clean and oriented properly as well. My only guess is that all the incoming and outgoing node connections to the joints could be causing the issue. How do you cleanly make a null group that works and doesn't affect performance? I want this thing to work like it is supposed to. Thanks for all your help!