Way back when I first started playing RPGs and D&D was basically all there was to play, a couple of players tried to have their PCs sleep in plate armor. They did so not because the GM liked sending in nighttime assassins, but because those players didn't want to face anything that *might* come upon our camp - like bandits (if we kept a fire going) or random monsters (if we didn't)  - in the dark in less than their full AC. Our GM allowed sleeping in plate but inflicted a -1 fatigue-based to-hit penalty, since the sleep that resulted wasn't very restful. On the other hand, he let you sleep in chainmail or leather armor without imposing that penalty. After a while, we learned to travel with enough hirelings to be able to set up a miniature version of a Roman legion camp (complete with light palisade and caltrops) and nobody ever had "bad sleep" issues again.