

Your ears can tell if something is coming from:
In front
Behind
Front right
Back left
etc
We don’t just percieve audio from left right so with 7.1 support an artist can take advantage of it and make different sounds come from different areas for a more full listening experience (though i doubt many actually do that)
Even some headphones can emulate 3d audio pretty well so it’s not an exclusive use for surround sound speakers
Nope sleep modes weren’t a thing outside of handhelds until the next gen