I have the same problem when maintaining Latex files in some RCS. After any "big" change (rewritten sentence, etc), I customarily reformat the text in emacs so

I have the same problem when maintaining Latex files in some RCS. After any "big" change (rewritten sentence, etc), I customarily reformat the text in emacs so that it looks nice on screen, which also totally messes up the diff. emacs has a mode which allows one "logical" line to wrap and to be edited as many "physical" lines, but when I tested it few years ago, it was rather broken. Fortunately, for editing Latex and such, I don't really need the diffs, I'm just interested in archival.