Singarounds need a shared agreement as to how they should work. Having someone in the chair is one way to do it. Someone with a knowledge of the people in the room, and an eye to recognise strangers and bringbthem in, can make a session special. But it can be done other ways, if people have a bit of sense and courtesy.

However it's done, it shouldn't be about control, it should be about support and enablement. (And occasionally reining in someone who needs it.)