last night I read about something called a VCA and looked it up. Then I compared it to an aux channel that I'm used to employing. I found a very informative webpage that quite clearly (IMHO) explained the difference. This stuff is still new to me so I find it exciting. Just one of the major differences between Garageband and Logic. Being able to group audio tracks into sub groups and controlling them with one fader.
Oops, it's on the other computer, I'll post this here and go to the other machine and add the link