story
Maybe I've just had a limited, poor experience with it, but from the apps I've used these functions are only available on the touchbar when the app is focused... which has the controls anyway.
I was using Skype for Business and it had the audio controls in the touch bar, and also on the screen about 1.5" inches above the touchbar. I wanted to mute and unmute when I had the app in the background, but I couldn't. Useless.