Sometimes you need more precise adjustments to your Mac’s volume. The volume up/down buttons on the mac have 16 settings, but if you’re in a quiet room sometimes even the first full setting is too loud.
I often listen to music in the office, but need to hear if someone says something to me. It’s just background music for me while I code or read email, so I want it to be really quiet.
If you need more precise control of your volume, simply hold down Shift+Option and then volume up or down. You will have a total of 64 volume levels (4 levels for each square), giving you the ability to get the volume perfect for your own needs.
Also, if you hold down just the Shift key while changing the volume, it silences the volume change “click” sound.