None at all, if you're setting them up correctly. 100-150 nits (cd/m²) is just about right. I color-calibrate my monitors and this is one step in the flow. I calibrate to 120 nits and find that it's consistently about 33% brightness. Calibrating this way, I can look at a full white screen (think "blank notepad window") with no particular eyestrain.

My issue with running most monitors this dim is that colors look so much worse and contrast is lost. It’s not as much of a problem on my OLED phone though, which does tend toward the dimmer side. My desktop monitors (IPS) on the other hand are rarely below 50%.