sometimes you're already too tired to make your way to the bed, so why not give in, close your eyes, don't even worry about turning the tv off, the couch is just so cozy...
I have always had a lot of trouble falling asleep, but for whatever reason I only have that problem in my bed-- some subconscious part of me feels like I *have to* go to bed there and that pressure breaks my circadian rhythm.
Falling asleep on the couch however is forbidden, decadent and delicious-- you are not supposed to have randomly conked out there so its powers to make you sleep are so much stronger. I consistently sleep better on the couch than in bed.