Now, when you mark message as done, it becomes unassigned. That means that when the contact writes again, every space operator is notified.
In my use case, I can image a better scenario:
  1. A new message is assigned to operator A
  2. The message is marked as done and assignment stays with operator A
  3. the contact writes again – it's still assigned to operator A, so he/she is notified, as well as the space host/supervisor/manager (a new role for spaces?) who is responsible for the space – but nobody else.
It's all about work flow :)