I don't know for sure, but I guess there's a way to have someone "playing" the videos and the lights of the show with the band. Again I'm not totally sure, but I guess Rush makes part of the shows this way, also part with the click. Anyway, I think its better without the click and backing tracks, it doesn't bother me if the live performance lacks some guitars, keys or vocals, like DT used to do. But, If the band can't play or sing the instrumentation or vocals like they think it should soud live, I guess it's better to play the show with guest musicians.