They are also sometimes used for kids with
sensory integration issues. To my knowledge, I don't think there is any "strapping down" involved. This is strictly something that assists in giving feedback about one's physical limits and parameters, which seems to help in focusing and self-control.
On another
page on that website, the analogy is mentioned of some people preferring to sleep with heavy blankets. I know that I myself cannot sleep without a lot of weight on me regardless of ambient temperature. For me at least, it has something to do with being able to "shut out the world" and all its distracting stimuli, which includes gentle air currents and subtle temperature changes.