It is an "open" group that anyone can join and contribute to. Posts are not moderated.
Topic range from announcements-
to the silly-
to serious conversation-
Some positives to the venue are that so many people already have accounts there and check it regularly, the level of real time interaction that can occur and the fact that there is a written record of the conversations that can easily be scrolled back through.
Those with Facebook accounts that have yet to connect with their Realms friends can also use it as a tool to find them. If you go to the main group page you can look at the member list (found on the upper right) and link to any of the 398 group members profile pages.