Is your bbPress installation returning 404 errors?
This is something that has been bothering me for the longest time. My bbPress forum installation which I use for theme support, among other things, was returning 404 errors in headers. These forums were integrated into my WordPress installation here so I could have the same layout, etc.
Google Webmaster tools kept reporting 404 errors for the forum URLs and the W3C Validator claimed the page wasn’t there at all. Google also couldn’t crawl forum pages, as the Googlebot couldn’t “see” them. All of this was going on while everyone else could access the forum just fine.
This only effects bbPress installations that are integrated with WordPress. If you don’t notice any 404 errors when browsing your forum this plugin is not necessary.