Futons are one aspect of Japanese culture that I don't really care for. Every time I go to Japan and sleep on a traditional futon I miss my Western-style bed.
I have never owned one but my sister used to have one in her home office. I had to sleep on it a couple of times and slept great. It had a cotton futon mattress which was hard but I actually liked sleeping on it. No one ever sat on it either.
That's 100% of what I am able to add to this futon conversation.
When I was in Okinawa and mainland Japan as a US Marine, there were parts of my ill-spent youth when the night-life meant hooking up with Japanese girls, so I flopped on a few futons every now and then on a tryst or one-night stands, etc. I was in women's apartments or dorm rooms and/or motel/hostel/hotel rooms that were so small that the futon was the largest piece of furniture in there. I knew women who had never in their lives slept on any kind of Western-style bed, only on various types of Japanese-style beds, and as such, preferred Japanese versions. Authentic futons (along with other Japanese beds) in Japan make the Ikea version look like child's play, lol.
They are to save space - you roll them up during the day. I have slept on them sometimes for months at a time. More comfortable than sleeping on the floor.
Benedict Arnold 