I've been doing it lately, assuming it will reduce the amount of crap I have to filter out after the boil, and it seems to reduce the amount of head I get during the boil (less chance of a boil over). ...
I've heard that adding cleaned pennies to the wort can help prevent boil-overs. I guess they could provide nucleation points- I dunno. Any truth to this, or is it just an old wives' tail?