I've been an avid member of several forums in recent years based around gaming and have seen the chat box or 'bawx' for short on a number of them.
In short - It's a place where members of the forum go to socialise, receive instant answers to problems or just chill-out. It can get 'messy' at times, but adding rules and regulations can help cut the clutter.
For example - I'd advise a 'post-count restriction' (i.e. signatures etc) on the bawx in order to reduce spam and the like.
Food for thought.