Originally Posted by Tom Stanworth
Some people organize their composition by using a basic frame of reference: the shape of the picture. Other people look at their subject and realize that it would need such and such format to look good. With your camera you are most of the time limited to using only one format at the time (square or rectangle). So starting from the given shape of your camera is a way to save time on re-framing the shot in the darkroom. If you want to make an 20x24 out of a 6x6, you will need to do a little bit more enlargement than if you did it from a 6x7, and that could make a difference on your finished product. It's actually not a compromise: you're trying to maximise the potential of your tools.
Your not understanding it has no bearing on whether it is or not a good methodology.