An excellent and well thought out article that explains a number of myths that have been built up around the Rule of Thirds: http://petapixel.com/2016/01/30/10-m...ule-of-thirds/
It also has some brilliant explanatory examples of other compositional concepts as part of the mythbusting along the way. I found it very informative on a number of levels and has made me think a little more about composition and how "rules" tend to shape our thinking around this subject.