One common case would be to download someone's weblog, where you'd want all their posts, and any news articles they've linked to... but you would NOT want the entire websites where the news articles are hosted, nor even anything linked from the news article itself -- you just want the single linked file (and anything that -p would get for it).
(Please CC me on any response; I tried to subscribe but I don't think it worked.)
Thanks, Anthony DiSante http://nodivisions.com/
