Chalk it up to twelve years of Catholic education, but when I hear the word "rules", I just kind of ... bristle. Yet I was hardly fazed when I was studying art and photography and "the rule of thirds" (along with many other theorems, constructs, proclamations, and paradigms) was displayed on the chalk board. It was the foundation of all the was beautiful, they said. It was passed down from our elders. It was dogma. And I ate it up with the passion of the true believer. (Remember, Catholic school, nuns, the works). And the truth is, it still guides me and informs my work, but it just doesn't... rule me anymore.
I guess the trouble started a couple years after I began working in studios when, after a steady diet of large-format film and the occasional roll of 6x7 medium-format (and, not so commonly at the time, the ungodly 3:2 format of the 35mm camera) I was introduced to the lovely, simple, gorgeous square of the Hasselblad. Now truth be told, I was taught to compose loosely with it, so that a rectangular-formatted image could still easily be cropped and printed from it. But phooey on that. The perfect square I saw in the viewfinder was nature at its best, rules be damned. Granted, it's an occasional treat and not appropriate every time and every portrait. But when it is, it's sublime. My portrait of Whitney C would have no power or grace composed in any other manner. It's just how I see things sometimes.
The rule of thirds (and the corresponding principle of "power-points" in a composition) is of course a viable artistic standard that can lead us down many a beautiful path. We ignore it at our peril. Honestly, I'm not an anarchist; I can conform to convention and "rules" with the best of them (again, think nuns.....) and we need to be mindful of their usefulness as guides, lest our work dissolves into some sort of expressionistic garble. But we can turn it on its head from time to time. A slight bend of the rule, or an odd juxtaposition within it, can make a more compelling and powerful composition -- or a disaster. It's a thin line that divides them, but it's delightfully fun to live on that edge.
So I figure, it's ok to learn and follow the rules, as long as you make up a few of your own as you go along. After all, it's your vision, your statement, your story. And nobody can tell you how to do that.
Not even the nuns.