[bluGill]

RTOS means that if you are listening to music and doing something else the music plays without issues (clicks). Take a modern 16 core computer and load it up such that the load average is over 200 and your sound playing will have issues. Of course realistically nobody loads their computer down that much, but if you manage to anyway like that you will have issues with sound. Because you won't though RTOS won't matter for playback. Still if you try you can cause issues without a RTOS - I leave this as an exercise to the reader.

As other have said RTOS is critical for live sound because there they have to make compromises that mean much less load is needed to cause issues. If you configure your sound playback with the same compromises you will see issues on playback - but for just playing music on a regular computer those compromises are a don't do that situation.