What is uncropped nature?
Who is not cropping it? Uploader or photographer? And how far will will we take it?
'Uncropped nature' is the tag used by people who believe that cropping or otherwise editing photos without the photographer's permission is disrespectful. We tag because it's a good way of letting people know they are safe to reblog, without having to check whether the photo has been tampered with.
More succinctly, it’s a tag populated by people who believe that honouring the original artist is more important than a perfectly symmetrical blog.