When auto-creating groups you can also choose to populate them. But you can only select one kind of role to populate the groups. It would be good to be able to select more than one role.
For example, in Sweden the students goes from Admitted to Registered within the first three weeks from course start, during which time they have lesser permissions in a course and are not allowed to perform any examining activities. That we controI with their roles in Moodle.
I would guess that other countries have similar proceedures, and that there are more examples on when this would be useful.