Why would multiple stereo outputs be assigned to the same Grand Master fader?

Assigning multiple stereo outputs to the same Grand Master fader is primarily done to facilitate the creation of sub mixes and groups. This enables the audio engineer to control several outputs simultaneously, making it much more efficient to balance levels when mixing.

By having several output channels controlled by a single fader, the engineer can adjust the overall volume of related sound sources seamlessly. This approach is particularly useful in live sound settings or complex studio recordings where multiple instruments or vocal tracks are grouped together for a cohesive sound. It enables greater efficiency and ease during the mixing process, allowing for quick adjustments without needing to manipulate each channel individually.

The concept of sub mixes comes into play when certain elements within a mix need to be treated as a cohesive unit; for instance, all the backing vocals could be assigned to one Grand Master fader, allowing an engineer to adjust their overall level in relation to the lead vocal without affecting other elements in the mix.