Michael Reichmann, a photographic artist for whom I have enormous respect and appreciation, wrote about this subject in 2007 in his Luminous Landscape website (www.luminous-landscape.com). I refer you to the specific article, Understanding Aspect Ratios and The Art of Cropping . He makes the point much better than I could. “[A]ny photograph is of necessity about ‘something’, and it is the photographer’s task to hone the image so that it contains, to the greatest degree possible, only that which the photograph is intended to be about.”
For Reichmann, the key question we as photographers should ask ourselves is, What is the real story here?
In his own words, Reichmann shares his thought-process that governs how and why he crops an image: When looking at a new raw file of my own the first thing I ask myself is that question – What is this image about, and what do I want it to say about the subject? Only when I have a satisfactory answer to this can I proceed to crop and otherwise interpret the image.
I love the images Reichmann posts on his website. They are tight statements of an artist’s vision, cropped down to the essence of what his experience impels him say.
Read his article. And check his website often. It’s a treasure house to explore.