EDIT: There is one for subforums but not one for threads or the whole forum
On many forums you have 'mark as read' for the whole forum or (if possible) for the separate threads themselves. Once you've gone through the forum/thread and have read, commented or critiqued your personal favourites or what you think you can bring legitimate critique to, it's then difficult to see if a new story/poem has been posted because the thread is still blue. With a 'mark as read', you can remove ALL the blue threads and then you know instantly that something new has been added beyond that point.
It's just handy!
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