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%.

I have never noticed that problem. But I always adjust brightness as part of a full color calibration, with ICC profile and everything, which probably makes a difference.

I will say that it took a bit to adjust to the first time I did it, but now it's painful to use any monitor at "full" 200+ nit brightness.

When I went from BlackBerry to Android (Samsung), I noticed the Android was much dimmer, though BlackBerry devices had gotten brighter. My experience is from 8700c through 9900 Bold.