I leave mine on in case one of my friends or family need to contact me. They don't generally phone me after 9.30 unless it's important.
One of my aunties used to be quite bad for random texts at stupid o'clock. I did leave my phone out of the bedroom at night then. The reasoning being that a random text was unlikely to wake me, but if someone actually phoned, which they were unlikely to do unless it was important, I would still hear it.
Now it lies on the floor beside my bed.