7z: What does the -r flag do?

The man page for 7z simply says

Do not use "-r" because this flag does not do what you think.

The only documentation I can find basically restates the same thing.

   -r[-|0]
          Recurse subdirectories (CAUTION: this flag does not do what  you
          think, avoid using it)

So, what does it do, and why does the author of this documentation think I think it does something else?

This is 7zip 9.04 on Debian Squeeze (i.e. pretty old).

From the 7-Zip user manual (chm)

Specifies the method of treating wildcards and filenames on the command line.

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