Its to help with drainage of fluid and air, and allowing the swelling to go down, I think it makes you less likely to stretch the incisions as well coz of the pressure at the sides. I think once you think the skin has mostly closed over and its not sore for you then you can lie down again, I couldn’t of lied on my back at first coz the pressure on my chest was uncomfortable, it took me about 2 weeks I think and the I just lied on my side for another week or so x