Shared midi controls global

Hi Michael,
what happens if i turn shared midi control global on or off?

Shared Layers are linked, that is, volume and pan follow the one operated. So each Layer knows volume and pan of all MIDI channels when set by other Layers.
Only if this preference is set, this will also set the Layer Volume and Pan controls if - and only if - those Layers are within the same Part, and output to the same MIDI channel.