OK, a bit of an exaggeration perhaps.
But here’s the thing: sometimes, as you’re producing a track there are spots where it’s important to automate the volume (fading parts in and out for example). The problem is that later on when it comes time to do a final mix, adjusting the level of tracks with volume automation becomes a real pain.
Sure, you can highlight the track’s automation and grab a breakpoint to move all the automation up or down…
…but that gets old really fast.
A better solution is to do your volume automation using something other than the track volume. This could be an instrument or device volume control, or the chain volume in a rack.
Using controls like these, you can volume automate to your heart’s content during the production process, but still be able to use the track volume to change the overall volume of the track when you refine the mix.