Turning on bot bit pixel support is a trade off of more precision colors vs higher refresh rates. So its a combo of what your vid card can push out and what your display can output.
You need to look up your monitor specs to see what the limitations are when using 10 bit color.
On my Display, the limitation is the top refresh rate drops from 120 Hz to 100 Hz. Since the vid card I have can't push 120 Hz to my monitor, I decided to use 10 bit color because, why not.