If you’re accustomed to the feeling it’s hard to sleep without it. My husband can sleep with no blanket, even without a top sheet, just completely uncovered, and I don’t understand it, except that he tends to be hot, and grew up in a very moderate climate.
For most of us who grew up in a cold climate, we are used to the feeling of a blanket, even multiple blankets. In Florida, in the summer, the blanket I use is lightweight, because of the heat, and it took me years to get accustomed to it. I still prefer a heavier blanket.
I know people who turn their AC very cold at night so they can use a blanket.