Benefits of sleeping in a sitting posture

Occasionally some buddhists monks will take up the practice of only sleeping in a sitting posture for an extended duration of time - sometimes up to 3 months. - What are the meditational (preferably insight-meditational) benefits of such practice? - How would one undertake such practice regarding posture and technique? I read that one could start sleeping 1-2 hours in sitting posture and then move to a lying posture. Then slowly increase the time sleeping in sitting posture while reducing the time spent sleeping in lying posture. Thank you for your time.