1. My iPhone is also my alarm clock, so I leave it on at night.
2. I work in IT, and a lot of emergencies happen at night, so I get texts in the middle of the night at least once a month.
3. From time to time I get family/friend texts in the middle of the night (especially group texts), but I mention to most people that I need my sleep & would prefer that they not text me at night when I need my sleep (and I NEED my sleep), although some people just don't get it. Luckily the iPhone has a do-not-disturb feature for specific group texts & whatnot, so if the first text wakes me up & it's not critical, I can just put that group into DnD mode.
I do not plan on working in IT forever; being able to put my phone into "sleep" mode at night & not being in a constant state of readiness mentally is one of the things I'm most looking forward to when that day comes.