Althought I can in theory (and from experience) agree with masukomi
's write-up - But
there is another side to sleeping with someone, based on the premise you actually like sharing a bed
with that someone in the first place.
Sleeping with someone, literally sleeping with someone can also be one of the most irritating and frustrating experiences lovers can have. If your sleep cycles don't match then as one of wants to stay and talk the night away, your lover will get progressively more and more get drowsy and irritable, and once you've both decided to go to sleep you've got to find the perfect lover's sleeping position.
This sleeping position is never constant and can change nightly, it must satisfy the requirements of providing intimacy without the pain of the blood supply being cut off to body parts, warmth without suffocating, and a fair and just distribution of the bed sheets.
The onus is usually on the guy in the bed to accomodate the girl, resulting in him staring up to the darkened ceiling as the covers get unconciously stolen and he gets steadily pushed out the side of the bed.
Just like any relationship sleeping with someone can be all roses and sex, but it does have bad points too.