One of the features I use regularly in the display settings of OS X is the adjustment of the gamma setting of my monitor. This is useful because it can lighten up dark movies when you are watching them on your Mac. The gamma setting is only available in the “expert” mode of display settings which has disappeared in El Capitan. Thankfully expert mode is still there, it’s just hidden. To get into expert mode on El Capitan hold down the option key when you select ‘Calibrate…’ in display settings.