Well, as have some others on this forum, I used to work in commercial photography, too. Mostly advertising. Frequently using models. I can't recall ever thinking, while looking at what I was shooting on the ground glass, "rule of thirds". I was aware that it existed. It never crossed my mind when I was working, though. I was thinking of what elements needed to be in the scene, and how best to compose them. I was usually working fast. Models are expensive. The only rules I paid any attention to when using human models was:
Never have the hips, shoulders, or cheekbones parallel to the film plane. Makes them look way too wide. 
Otherwise, I shot from the hip on compostition. If I liked it, I went with it. And judged my success after processing all the "chromes".
I don't think that there are any hard and fast rules of compostion, other than to keep it interesting!