I grew up sharing a room with my younger sister. We argued like crazy, but we were also so close growing up. The arguments were mostly over bedroom space and bedtimes, that was it. I got my own room when my older sister moved out when I was 16, and have had my own room since (my younger sister doesn’t live with me anymore though). We couldn’t afford to have a four bedroom property, and so it was my older sister in a room by herself (3 years older than me) and my younger sister and I in a room (she’s 2 years younger than me).
My younger sister and I would stay up late talking, watch films together, generally have fun. But due to the age gap (which isn’t even big, but when it’s an 11 year old and a 13 year old, it feels like a huge gap) we argued like mad over bedtimes as they were usually at the same time (which I hated), but obviously that didn’t become an issue when we got past our tween years.
I never knew any different growing up, and I liked the sense of security it gave me sleeping in a bedroom with someone else. I was never alone, which was usually a good thing but when I did want space I had to go and find it elsewhere, which got irritating real quick.
For my own kids, I’m not bothered. I’d like them to have their own nursery, but if money doesn’t allow me to give them their own rooms, then the girls will share and the boys will share. I think this varies depending on whether or not you grew up sharing a room, well it seems to be so going off this thread!