We have a lot of courses from different semesters. We're planning to archive old courses, of course, but there's always a period of time between each semester, where courses from different semesters must be shown.
For example, a teacher might have 15-20 courses for each semester (30-40 in total). Filtering between semesters would therefore be quite useful for organizing, and finding the right course.
(This function is implemented on several other places in the system, e.g. the admins or in the self-registration for courses.)