Since it’s always running, it will stay how you set it until you restart your computer, at which point it will match itself to 100% of the master volume. The only exception to this is the System Sounds volume.
Each time you launch an app, you’ll need to set its relative volume again. While setting individual app volumes can be really useful, there are a few limitations to keep in mind: The level you set for each app is relative to the master volume, so as you change the master volume, the volumes for each app also change.
The Device slider controls the master volume.
