I don't think it is so much stating a "rule" but rather saying why one does anything in such and such way.
For example someone might ask "What is the best batting for Hand Quilting" And then 15 different answers are given all with different batting but often no one says why. I usually say that when someone says you gotta, you must do it this or that way......to ask why. I can then make a decision if it right for me or I want to try.