@Geo you don't need to sleep, but it can be useful if you want to advance to a certain time/day quickly. if you know an npc is going to be in X place at X time, it would be very annoying to have to sleep like 4 times at the same inn to advance to that specific point. but physically walking to your room and everything is cool if you're really trying to get into the immersion aspect of it, which i did in skyrim when i had a mod that required sleep.