Another reason hinted at, though not expressed in so many words, is where
the content represented by one URL exists in more than one format, where
HTTP content negotiation is normally used to determine which file is
retreived, yet the person who built the link wants a particular version of
the file.
<A href="grad_paper" content-type="application/postscript">This is the
postscript version</a>, and <a href="grad_paper"
content-type="text/html">this is th HTML version</a>.
A better example would be one where the person making the link has no
control over the URL source, thus unable to give them different names.
Brian