I've slept by myself, except for rare exceptions, for almost nine years. I should amend that to say I did sleep with my cat, and a great partner she has been. Quiet, respectful of my times, whims and quirks, and she doesn't grab the pillows.
For the past few months I have also been sleeping with my non-feline SO. And besides the obvious benefits, which I don't have to elaborate upon, so many aspects of sleeping with someone else change your own sleep patterns and behaviors, and not all for the better.
I used to wear any big T-shirt and fall into bed, I now have to prepare myself. Shower, perfume, cute nightshirt, teeth flossed, hair brushed. No more happy slob with bed head.
In the past, if I wanted to stay up in bed till 2 am I did, with reruns of Housewives from somewhere or other putting me to sleep better than an Ambien. Now, my partner goes to sleep by 10 pm. If I did that too, I'd be awake at 5 am. So we compromise. I stay up in another room and he goes to sleep awhile and wakes up (kind of} when I come to bed. This has meant less sleep for both of us.
I used to keep my laptop, iPhone, Kindle, assorted magazines, books, robe, fruit, crackers, jerkies, mechanical devices, notes, trays and miscellany scattered around the bed. You would have had trouble finding me. Now my bed looks like an empty canvas ready to be painted. This is good, except that all of that stuff usually winds up under the bed. Often with the cat.
He likes a hard pillow, a warm room, shades down. I prefer the opposite. We have tried all permutations and are still working on it.
There are lots on both sides, and the kitty adds hers, too. I have gotten used to most of them and have been adept at muffling or postponing my own, but my cat has awakened on many occasions with a shriek. Noises are not conducive to sleep.
Fun. Intimate. But can go on till the sun comes up. Less sleep.
When the someone who shares your bed wakes up, chances are you will too -- at odd hours of the night, as well as early hours in the morning. Not good if you're a light sleeper.
That said, cuddling and spooning are a couple of the nicest and easiest ways to fall asleep. (And that's with my cat!) My beau has learned to take the other side of me, and I wind up most nights in a man/kitty sandwich, and happy to be so. And then, there is that aspect alluded to in the second paragraph. That makes up for the downsides, and definitely aids in sleeping. But not for the cat, who feels left out and usually runs away, meowing as if I had stepped on her tail, which I often do when I wake up at odd hours and head for the bathroom.