I always find this a bizarre debate - photography is an artistic process, and how you place your subject(s) in the frame and the size and proportions of that frame are all part of the same compositional dynamic to me. If you only have a 35mm camera to hand but your subject requires a panoramic or square crop to give the most visually pileasing result, why would you not do that? Given a choice betweem a tightly framed, balanced composition and one that loses impact because of wasted space in the frame there's no choice for me.
I understand that some photography teachers require students not to crop so they can learn to compose effectively, think about the corners etc., and that makes perfect sense. There may also be good presentational reasons to have all your shots in a series in one format, but otherwise why tie one hand behind your back, artistically speaking, if you don't have to?