Most one night shows who do not tour with a PA of their own require the house to provide one of adequate quality. They will usually specify that it must have certain facilities. Very often the artistes consider the monitoring system one of the most important facilities present. Some may even require reverb to be included in the monitoring system. A good general purpose house system should be able to offer two separate, controllable channels of on-stage monitoring, independent from the content of the main house system.
Normal usage requires one channel for the main artiste with the other used for the backing band.
Even if the artiste is performing to backing tapes they will need the music through the foldback to sing to. It is a fact of life that many artistes spend more time on the monitor sound than on that for the audience. On small mixers the balance set on the individual channel faders is then combined into a left and right master output. This system is extended on large mixers by the introduction of grouping. Imagine the case of a rock and roll band.