its a way of "bumping" up the thread to the top and the first page, so more people will see it, since with every post that thread automatically goes to the top of the list in the forum. So by leaving a *bump* it serves its purpose. Usually people do it for unanswered questions to get more views by someone who can possibly answer, or just something people think is important for others to see. this makes sure more people will see it, instead of having to go to page 4 to view it.