Course Sets are (often?) used to implement Subject areas (Departments, in some nomenclatures.)
Subjects come and go, and are renamed.
Often the lifecycle of the Subject area is subtle - for example new Courses will not appear in Enterprise feeds for the Subject area until a certain date. Yet the Subject area itself must be defined.
During a Rename of an existing Subject area all the prior Offerings must remain 'wired.' The Prior CourseSet has to stock around, and a new one be added. That's fine. However the retiring CourseSet should not display anywhere which allows Site Creation.
This can be handled by using the Start and End dates for CourseSets, and honoring them in the Sakai UI.