I have joined quite a few groups and they are all listed on the chat sidebar. They take up enough space that often I cannot see all of my friends that are online. Additionally, many of the groups almost never have anyone in the chat.
As far as I can tell there is no way to remove groups from the sidebar or change the order they are in. I think that this would be a welcome addition and would make chat much more useful for those of us who are members of multiple groups.