Multicasting only "saves bandwidth" if you are replicating identical data to a group of destinations. For instance a retailer might wish to distribute video accross their network to their stores for advertising in store. Rather than each store opening a unicast connection, requireing that the server duplicate the video data into each session and the network carry multiple copies of the same data, the server multicasts the video and the network is responsible for replicating the multicast packets to any registered sources. So the only data duplication occurs at branches in the multicast tree, and even then on ly one copy goes out of each destination link.
The same idea is used in distributing software to workstations, for instance.
It can help in video conferencing where there are more than two participants, but unless you regularly VC with say half a dozen or more endpoints the complexity of setting it up may not be worth it.
