Support for multicasting, wide coverage range and high bandwidth, makes WiMAX a leading solution to deliver bandwidth-hungry services like IPTV to mobile subscribers. The smallest logical bandwidth allocation unit in OFDMA-based WiMAX is a slot. In this article, we use the term slot to introduce a new performance criterion, called multicast gain, which can be used for computing multicast efficiency. We analyze multicast transmission for delivery of live TV channels in WiMAX-based access networks, and determine the gain to be expected for access links in order to quantify the benefits of multicasting. We show that for unpopular TV channels, using unicast flows can be a better choice.