http://en.wikipedia.org/wiki/Multicast shows(suggests?) that broadcast is also time-efficient since sender only does one send. However, multicast is smarter and more bandwidth-efficient.
IPv6 disabled broadcast — to prevent disturbing all nodes in a network when only a few are interested in a particular service. Instead it relies on multicast addressing, a conceptually similar one-to-many routing methodology. However, multicasting limits the pool of receivers to those that join a specific multicast receiver group.