I have a much-too-long-for-one-comment write-up about this, but it's basically for those who build SCMs or tools that need to work with SCMs. End users shouldn't have to care about this.

There's not one patch/diff format. There's often at least one per SCM. A couple are pretty good (Git's), many are okay (Subversion's), and many are really bad or non-existent.

I founded one of the older code review products, Review Board (turning 20 next year), and we deal with the problems this is trying to solve all the time, across over a dozen SCMs. So we're the ones complaining :) And much of this is based on extensive feedback from SCM vendors we've spoken to about this at length.

Most people shouldn't have to care. But it benefits tools like ours that have to deal with the nightmare that is the world of diff formats.