Good input, Natja! I think you are spot on--it depends on what everyone wants and needs. And those needs may change over time, so nothing is ever set in stone.
I know when ES first moved in, we always slept in one bed. We soon learned, however, this was not practical for our family. I toss and turn, we all snored something fierce, and if the person in the middle needs to get up to use the bathroom, everyone gets disrupted. I had to get up early for work, so my alarm would wake everyone. We had to adjust to meet everyone's needs.
Currently, we are living in a VERY small house: 4 adults, three dogs, and 4 cats, though the cats spend as much time outdoors as in--and so do the humans for that matter. It can be very claustrophobic when all four of us are in the living area. Not surprisingly, we tend to pair off in different combinations in different areas of the house. I tend to spend a lot of time on the front porch when it isn't too dang hot.
For our intentional family, if money were not an object, we would have a home built with three separate wings, and a large common area. That way, we could all have our own spaces, while enjoying the comforts of ample shared space (living area, kitchen, dining room). That would also give us each the freedom to have a space to express ourselves. In that aspect, we are the extremes.
S likes lots of reds, pinks, and oranges everywhere. Currently, her living room is orange-red (walls and ceilings alike) Her kitchen in red (walls and ceilings), her bathroom is lavender (ditto), and her bedroom is bright (BRIGHT) yellow. Every inch of her walls is covered in artwork. It is beautiful, but it gives me sensory overload. With Bud being bi-polar, he is ultra sensitive to all the visual stimulation, so we don't visit S nearly as often as we would like (2-4 times a month). K, however, likes the stimulation and sees S 4-5 times a week.
K is somewhere in the middle. She likes dark colors: living room (walls and ceiling) are a dark chocolate brown, and the kitchen is midnight blue (walls and ceiling). She does have brightly colored artwork on the walls, but as the rooms are already small, and there is not much natural light, at times, it seems tomb-like.
I am the other end of the spectrum. I like the illusion of space and light. I tend to paint my walls and ceilings light colors, and insert pops of colors with artwork, throw pillows, and rugs. For K and S, this is too stark. If Bud has his way, everything would be white, there would be no visual stimulus on the walls, no clutter whatsoever.
We had initially though separate homes on one property would be the way to go, but it seemed too disconnected for us. If the universe looks kindly on us, we will one day have our big house with separate wings. Until then, we make do with what we have.
Bottom line, as Natja stated, it is very dependent on the family involved and what each individual wants and needs. The trick is assuring there is constant communication and feedback from all the members of the family. Had Bud, ES and I not sat down and re-assessed sleeping arrangements, we would have made each other miserable. If we all wanted to pile into one bed for sex, or if we wanted to have a nice snuggly nap, that was fine. But for quality sleep, one bed was not a practical, viable solution. We adjusted accordingly.
Find what works for everyone!