The web BOT's troll through webpages online every few weeks and find links on the site and other sites that could link to this site and move this site up on Google or Yahoo. Which could definitely be a good thing.
You can see how well they work by posting to a thread and later in the day or sometimes within the hour if you do a search on Google or Yahoo your post will already be listed. On one occasion it was minutes later I found one of my posts.