I usually have my phone at 0% brightness, but that I can still see something is a clear indication it's not actually 0%. The screen is still too bright for me if it's the only light source. Same for audio; I basically only switch between mute and minimum volume because everything above is too loud for me.

I hate that there's no way to acess more fine-grained levels below the arbitrarily imposed minimum. I realize most people would think their phone is broken if they could get it into a state where it doesn't produce any perceivable output despite not being explicitly off. I just wish there were some secret handshake I could use to confirm that I'm okay with having to find the brightness control while not being able to see anything; I already do that when I'm outside in the bright sun.