When I was in College I was taking a color photography class. Like many, I was obsessed with the rule of thirds. At first during our weekly slide review and crit my images were very well received. They were colorful minimalist abstracts taken at an abandoned mill just outside of town. Lots of decaying wood and colorful metal tanks which at one time held some sort of dyes. They were very well composed, and I kept getting a of of compliments about that.
But as time went on, the crits because tedious and even I found myself falling asleep to my own slide show! Midsemester drowsiness aside, the collection which was once very inviting and receiving great feedback was now bland and noteworthy. At the end of the semester we had to submit several slides which represent our best collection of images to the professor. He must have been prepared because he immediately took my slides and placed them on the light table, flipping a few, rotating the others and then stacked them up. They lined up strikingly well.
It turned out the entire semester I was taking the exact same composition in various orientations! They were "perfectly composed" no doubt, but that was exactly the problem. I reduced what makes a good composition to a formula which I had replicated over and over with mechanical precision and I think that if you go about looking at these "rules" you'll eventually get down to a single most efficient outcome that can be applied to almost any situation - and those which do not fit you start writing off as it not being a good subject. From my experience it starts to become a situation where you seek out the composition before anything else - it gets easy and you get lazy.
That same professor told me the next semester that the best thing to do with composition is to learn it completely and then forget everything. The idea is that you'll know when and how to apply conventional composition on a more intuitive level.
Another issue which I have with these composition guidelines is that they are designed to convey harmony and balance. Often though I seek to convey tension. Take for example these two images which follow traditional composition:
In this image I was struck by the symmetry and balance of the subject and;
This image I was struck by it's delicacy and stillness. In both images I chose a composition which best conveys these ideas. However these compositions have a different effect on the image:
In this image I was interested in conveying the idea that everything decays, juxtaposing the rubble in the foreground with the functional building in the background. To convey this tension, I obstructed the more recognizable subject.
In this image I was interested in the absurdity of the situation. Here I found a flyswatter on the sidewalk positioned over some utility markings. I was struck by how the flyswatter lacked it's function when taken out of context, and how in some ways without the context of the sidewalk the markings have no meaning - together, it's just a jumbled mess of meaningless data. To convey this contextual dilemma I again chose a composition which is best suited, one where the eye really has no where to go.
Composition should be seen as a tool to convey ideas about the subject. An image where the model's arms and legs are cut out of the scene will not convey a sense solitude or complacency, it will convey urgency, feeling restrained or boxed in.
So I think it's always going to be OK to break the rules, so long as you aren't just doing it for the sake of doing it, and choices which you make regarding composition should reflect what you're trying to convey.