phranque - 11:41 am on Mar 29, 2012 (gmt 0)

if someone links to your content in an unflattering manner you might not like how google shows that url & snippet in the index.
the snippet might be url-only but it might also be constructed from the anchor text and/or context of inbound links.
robots.txt exclusion might also prevent canonicalization efforts since an excluded url will not be requested and therefore will not see a redirect response.