what is the advantage of having a large surface area?

Gas exchange surfaces tend to have the adaptation a large SA:volume ratio. This is advantageous as it increases the area over which gases and other materials can be transported into and out of the organism, via diffusion and active transport. An example of a gas exchange surface with a large SA:volume ratio is the alveoli (air sacs). There are many alveoli in the lungs, creating this large surface area for gas exchange.