Imagine a gradient bar of red, green, or blue on a display. The latest displays show so many colors that the 256 shades in an 8-bits channel will show banding.
Banding is horrible for photo/video editing hence 10 bit displays that can show 1024 shades in a single channel which is more shades than our eyes can see.
HDR in gaming also uses 10-bit per channel, but it's often a gimmick with current cheap gaming displays and might show banding even if there are technically 10-bits. OLED gaming monitors should be able to display 10-bit accurately though.