Nested VCA Faders
VCA faders can control other VCA faders.
If you use several VCA faders that control different link groups, you can create another VCA fader that controls the VCA faders. This allows you to control the volume level of several link groups at the same time.
Technically, a VCA fader that controls other VCA faders affects the volume level of all VCA faders and linked channels.
Example
A VCA fader (main fader) controls a nested VCA fader that has been set to -10 dB. The latter VCA fader controls a linked channel that had an original level of -3 dB and that is set to -13 dB. If you change the main fader level from 0 to +4 dB, the controlled VCA fader is set to a level of -6 dB, and the linked channel is set to a level of -9 dB.