Reduce in Bus Format. What does it do?

Hey just curious cause it has bugged me for a while and I can't find any documentation about it.

Does anyone know what the Reduce checkbox in the Bus Format page does?

Busses in réduction mode are intended for routing to more than one fixed channel format, such as simultaneously creating 5.1 and LoRo mixes.

Please forgive my ignorance on this, but what exactly is different about the bus when I select that? Does it change the volume or the sound at all or is it changing the block size or some other hardware selection?

For example:
5.1 Music Submix Buss (Reduce enabled in the Bus Format window) > Stereo Main Mix Buss

The Reduce function follows the ITU standard for the LoRo mix:
Lo [Left + Centre (-3dB), + LS (–3dB)]
Ro [(Right + Centre (–3dB) + RS (–3dB)]

The LFE is obviously discarded.

This is soooo helpful! Thank you for indulging me!