Every time I use add-apt-repository, I get a bunch of .save files
under /etc/apt/ and I’ve never found them be anything but identical
with the original files. It would be good if add-apt-repository only
wrote .save files that are not identical to the originals.

This is not really just a wish list item.. touching files in /etc by default,
without asking or telling the user, is not ok. Furthermore, the files are
recreated, messing up both the mtime and ctime metadata. Just sayin.

It's a graphical editor for sources.list files, so it is obviously
OK to edit sources.list files.