I dunno. Staying in an Airbnb in Seoul, I woke at ~1am to someone banging on my door and yelling for about five minutes. Pretty sure if it weren't locked, I'd be in some sort of trouble.
From another angle, I've been to a restaurant in a central part of Seoul where the owner kept his cash in a wooden box with no lock by the entrance. Pretty sure anyone could have grabbed that box and ran out the door, especially when the owner is in the back preparing the food.