We have a particular discount structure for course purchases, for example, 20% discount for 100+ course purchases. A minimum usage setting in the coupon set up would mean clients could not use the coupon for any less than the 100 users the specified discount applies to.
Similarly, we have a classroom edition of a course that requires a login for a teacher and 30 students. Because users cannot purchase one course and receive multiple logins, we need to be able to set a minimum number of purchases for the course. For example, the course could cost $30.00 per person for a minimum of 30 users. With not minimum amount able to be set, users can purchase the course for one person at this discount rate.