Natural light is healthy, it's better for both mental and physical health. I generally keep my shade about half or a quarter open, so I can see the view and benefit from the light while making an effort to restrict it to my seat as much as possible. If you need complete darkness to sleep, you aren't going to sleep well on a plane whether I close my shade all the way and make myself feel awful or not. It's never going to be completely dark or completely quiet on a flight, if you're a fussy sleeper you're going to have a problem no matter what.