When quitting one application, quit additional ones I'm trying to figure out a way to do the following: when I quit Logic Pro X, I want to also automatically quit other apps that I use with it, as they are no longer needed. Is this possible?
You can create a simple Applescript to quit the other apps. To do it, open Script Editor and type the following:

tell application "AppName1" to quit
tell application "AppName2" to quit
tell application "AppName3" to quit


Save as Application.

Then when you quit Logic Pro, you just need to double click on your new app, and it close all your defined programs.