How might you use this facility? 

A good example would be a school or club who wanted a web site but also wanted their pupils or members to contribute to it.  Each pupil or member would be assigned a username and password plus, most importantly, a level of authority relating to what they could update.  Thus a pupil could add comments to a topic initiated by their teacher and those comments would carry their personal identifier.  Similarly a club organiser could begin a topic and club members then add text and pictures to it.