When you are supporting Wireless Applications that require MC, such as Spectralink's (ca use MC for registration as well as Push-to-Talk).
However, it is a common mistake to use the same MC group that your application uses.... Wrong! The WLC controller actually uses the configured MC group to distribute MC traffic to the joined AP's, so you really want to use a group that is not used by the actual applications.
(don't forget to rate all responses)
