If you’re a PulseAudio user on Linux, you might have experience this feature: When you change the volume in an application, it changes the system volume at the same rate.
This feature is called “flat volume” and seems to be targeted to users who do not understand the concept of a mixer. For example someone might turn up the volume of an application (i.e. Spotify or Youtube) all the way up while the system volume is very low or even at zero and wonder why “it” isn’t working.
On a first glance, this might seem reasonable. However, speaking from personal experience, it’s actually physically dangerous. Some applications take pro-active control over the volume (for example Zoom). If you’re wearing headphones and some application forces the volume to 100%, you might be in for some ringing ears or even permanently damaged hearing.