I try to keep my iPad on the lowest, or a little bit of brightness, and on night shift. Really helped my eyesight. Same on my laptop, except there's no night shift so my eyes get weary after using my laptop for some time.
on my phone, i always keep it really low since i'm super stingy w my battery (no tabs running, low power mode, etc etc). i rarely ever go over half but i normally keep it about a fourth of the way up. on my computer, it's pretty low too, just because my eyes are unable to handle the screen if it's too bright.
On the computer I don't really change it, because it's always when the lights are on that I use it anyways, but with my phone it depends, in the dark I'll have it lower and higher of course when I'm in the light. I don't like having it on super bright though cause it bugs my eyes.
when i'm charging my phone, i have it all the way up. when i'm not i usually keep it all the way down. i don't want my phone to die, since when i'm not charging it i'm usually very far away from a charger that i can actually use.
It's always on 25% or lowest because I'm usually on my phone indoors and it's not necessary to have it any higher. The only time I turn it up is if I happen to use it outdoors. I get headaches when it's too bright :/