It's just a way of keeping a post up near the top of the list of posts so people will see it! As posts get replies they become first on the list and the other posts get moved down the page, if an unanswered post gets pushed onto the second page by lots of new posts or answers to current posts it's unlikely to be seen so moderators (or anyone really) will "bump" it up so that it doesn't get lost and hopefully someone who can help will see it and reply properly.
Hope that makes sense!
Laura