Set a super-quiet volume level
If you work with your laptop in public spaces, or listen to music on headphones, you may occasionally want the lowest-possible volume on your speakers or headphones. You might think this is simple—just decrease the volume until you’re at the lowest-possible setting (i.e. only one “block” illuminated on the onscreen volume control). But there’s actually a “super quiet” setting that’s a notch below that one.
To access this super quiet mode, use the volume keys on your keyboard to manually set the volume to zero—this trick won’t work if you use the slider in the menu bar’s volume controller. Your Mac is now effectively muted, which you can check if you have external speakers with their own volume control. Turn the speakers’ volume control all the way up, and you won’t hear anything.
To access the “super quiet” mode, press the Mute key on your keyboard. Bingo, you should now hear (very faint) sound from your speakers. If you press Mute repeatedly, you’ll see that the onscreen volume control still doesn’t show a set volume level (none of the bars will be illuminated), but you’ll definitely be able to hear the audio muting and unmuting, assuming you’re in a relatively quiet location.
This may not be useful all that often, but for those times when you want the quietest possible sound, it’s quite handy.