Michael Mulich <michael.mulich@gmail.com> added the comment:

The wiki page has been edited to note what the develop command will
write to the file system. I'll restate it here as well...

The develop command writes three pieces of information to the filesystem:
 1. It calls upon the build action(s) to build the package relative to
the package's root directory.
 2. It calls the [build|install]_distinfo action to write the
.dist-info metadata inside the build directory. (see also Issue 12279)
 3. It adds the build directory's path to a .pth file.