I dont understand how anyone can have a rule or why they would try to consciously compose to a format, as this is a comprimise from the outset. For me, each image is dealt with as a unique visual experience and cropped in such a way as to communicate that as best as possible. I recently sold my TLR, but my images where all sorts of shapes as determined by what I felt was 'right'. I cannot comprehend any other approach as what would its purpose be other than convenience, which if important to a person, is fine. I sometimes have left images uncropped for speed and ease when doing basic record stuff, but I would not claim that it is more 'literal' or 'honest'. The only issue that does impinge upon my printing is that stubby rectangles are for me the hardest to frame and look pleasing. Squares are easier (whether in squarish or rectagular frames), any normal rectangle is easy as are panoramas, but stubby rectangles to me always look a tad clumsier on the wall, especially when large, so I tend to limit the enlargement if a stubby rectangle is the 'right' crop. Personally I often stick to the uncropped square format for portaits, esp environmental portaits/people, but for dedicated landscapes I would mainly crop to varying degrees.