The VC-2 goes beyond basic vocoding: it also uses digital models of real choral ensembles and human voices. And unlike a traditional vocoder, where you have to supply a carrier tone to give the microphone signal its pitch, the VC-2 provides the carrier itself. Just press a key, or send MIDI notes, to change the pitch of the vocoded sound. That's useful for classic vocoder sounds and especially handy for choral modeling.
The VC-2 can also work as a traditional vocoder: its Processor 1 and Processor 2 modes take a carrier on one input channel and your microphone on the other.