VCA’s have no signal passing through them they just control track faders they are linked to (thus DCA makes more sense - digital controlled amplifiers) the name VCA harks back to analog consoles (voltage controlled amplifiers)
The big deal to remember IMHO and to understand is the advantage of VCA’s
is they don’t destroy your FX balances, because …
When you normally use a track FX send it is normally post fader, meaning when you lower the track fader the amount of signal being sent into the FX send is proportionally raised or lowered.
So if you then sum ten drum tracks to a stereo group and use the group fader to control their overall level you just made all those track FX sends PRE FADER.
So now as you lower the group level the FX are still being sent out of the individual tracks at the same amount and your FX balance is destroyed.
VCA’s prevent this from happening, by controlling a group of tracks faders linked to them before they are summed into a group.
It is worth remembering if you do insert a compressor into a group and set it’s threshold, when you use VCA’s or any individual fader to change the level feeding that group that the threshold will have changed.
Therefore personally I tend to avoid using groups at all and simply use VCA’s and insert compressors on a per track (mono or stereo) basis.
For instance I’ll put a stereo compressor across my drum overheads and say an 1176 on my snare and an optical comp on my kick(s) but not an overall insert compressor on a group being fed by my drum tracks so I don’t need to worry about group inserted dynamics thresholds as I mix.
Yes you can just link the track faders using a simple link function but that won’t let you easily change an individual track level without constantly bypassing that link.
Plus you can nest VCA faders, another cool feature of VCA’s (a VCA’s controlling other VCA’s)
Also and importantly a simple track link function won’t allow you to trim already written track automation the way a VCA fader will.
VCA faders allow you to trim already written automation which is a “BIGGIE” of huge proportions.
Hope that helps a bit.