For those who are wondering what the big deal is, 10-bit color means that more details can be displayed as opposed to 8-bit color which is usually the case in most displays. In particular, 10-bit color support helps to reveal soft gradients better so that editing such sections of a photo or a video will be more accurate.
So like we said, if you’re someone who needs to rely on more accurate colors for their work, then this feature might be worth checking out. Unfortunately for now it seems that only the 4K and 5K iMacs from 2014 or newer have that feature, so if you’re running an older iMac it looks like you’d be out of luck.
The 10-bit color will also only work in OS X Preview and the Photos app, at least for now. More mainstream photo editing apps like Adobe have yet to take advantage of this support, but we expect that will change in the future.