Precisely adjust Display Brightness
Hold down the Option+Shift keys while you adjust screen brightness to precisely adjust the displays brightness by allowing you to have 64 levels of varying brightness vs the default 16.
As you can see in the screenshot, this is done by breaking each brightness step into four stages. I find this kind of precision really useful on my MacBook Pro when in dimmer lighting conditions.
You can do the same type of precise adjustments when changing your Mac volume levels.