Are you a vampire?
Nope, it makes a big difference to how much your room heats up during the day which in turn makes it easier to sleep at night, seriously if you suffer try it! I only do it for the bedroom the lounge etc all get opened as it doesn't matter if them get nice and toasty.
Same for leaving internal doors open, we all get conditioned to close them to keep the heat in or for privacy and the number of people who close the bedroom door and then moan about being to warm is ridiculous!