I'm in the middle of redoing some of my pro tools templates and was wondering if anyone could explain the advantages of using a VCA over an aux track to route my submixes to?
Using an aux track would require you to re-route the audio of each track involved into the aux, and recording automation on the aux track wouldn't affect the automation of the sub-tracks. The VCA is purely a control- and automation-based system, meaning 2 things:
Your choice should depend a lot on a your workflow and preferences for signal routing. In my experience, VCAs are great for categorizing numerous independent tracks and giving you a single handle for that "category".
audio isnt actually routed thru a vca, its essentially virtual but you can automate a vca and later choose whether to merge the vca automation into all of the source tracks or not...
on some systems you cannot scrub or varispeed audio when it is routed thru an aux, whereas you can when its controlled by a vca - i find this very handy when editing
VCA Master changes will affect to Volume-fader values for each track in the group, so Send Levels wich are in post-fader will be affected too.
You cannot add inserts to a VCA since there is no signal routing happening, so if you need group processing I´d use Aux Tracks.
Or you may use both: that is, just group tracks levels into a VCA Track and route their outputs through an Aux Track. This way you can add inserts and while you have control over their fader values.
I personally don't use PT much, but I did recently see this video that I think answers your question and gives some good examples of the differences:
One advantage of using a VCA is that it doesn't affect your available resources like an Aux track does (VCA's aren't processing audio). If you have high track count projects or low system resources it might be worth considering using VCAs wherever possible (until you need an Aux for group effects, monitors etc). For smaller projects it won't make much difference.