Samsung Display (which makes display panels, but not actual monitors) showed off a 27" 5K OLED 220 ppi display.
For HDR for example. It bears repeating yet again, even if the average screen brightness is set at say 150 nits in a light controlled room, you still may want to have highlights at 700 nits for some content, but that 700 nits stuff may only occupy 2% of the screen. Movies are mastered to 1000 to 4000 nits, so if your max brightness is 400 nits, then everything from 400-4000 nits is completely lost in a sea of white, unless you compress the brightness levels (tone mapping) to match the display. Meanwhile, some video games are mastered to 10000 nits.
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Or you may work in a very bright environment. A setting of even 250 nits for overall brightness may be inadequate.
I'm curious. What are you colouring?