[f1shy]

There are cases where you want to have 2 applications running and playing sound, and want to set the relative volume of each...

[hdgvhicv]

That’s what your system volume app does - each process outputting sound has its own slider and you can mix them at various levels.

[XorNot]

I mean technically that is a system level feature...and there's nothing really wrong with an application adjusting it's own volume as defined by a system level volume setting for that app.