+1 for this feature. I can think of a use case where if you are teaching a course that has weekly classes on different days (e.g. 1 class is every Monday, another class is every Tuesday, all in course A100), then a group can be used for all A100 students where each Monday/Tuesday class are separate groups within the parent group.
That way, announcements/course materials for the whole course can be sent to the parent group, while individual days’ classes (e.g. the Monday class) have their own Q&A category.
Sorry for the long and confusing analogy!