Song recording on Yamaha instruments

I have a Yamaha CVP-805 which I enjoy very much. I am trying to understand the logic behind its MIDI record module. Why is there a "right-hand" part and a "left-hand" part that I need to record to? As far as I understand, the only thing that matters is the 16 MIDI channels. What did Yamaha mean by giving me a "left hand" part and a "right hand" part. I think the most intuitive way (for me, at least) is having a channel number and a voice, then I can just "go at it". Can anyone explain the logic?