I leave it on, BUT, I don't have it near me. Instead I plug it in to charge up while I sleep
I can't sleep well with my smartphone next to me - it messes with me (headache, uneasy sleep, bad dreams, ...)
I do however own a small smart-watch that I do wear while I sleep, because it measures my sleeping movements and time (which is practical for me since I'm sometimes so confused, that I want to stand up after only 2 hours of sleep - so checking my watch tells me if I slept enough already or should go back to bed quickly!), but again, I switch the Bluetooth off, so it doesn't send out any signals ^^