What is the advantage of the small intestine being so long and having villi?
The small intestine is so long and coiled up with numerous villi to efficiently digest the food.
The diameter of small intestine is about 1 inch but the length is about 10 feet.
The large length gives a sufficient time to the body to digest the food and extract maximum nutrition while the numerous finger like projections called villi along with micro-villi increase the surface area for absorption. This absorption area is increased because the food is now in contact with more of the cellular area. It is estimated that there are around 130 billion micro-villi per square inch in the mucosa of the small intestine.
P.S. Mucosa is the inner layer of small intestine that absorbs nutrients from chyme.
For detailed information on small intestine, you can check this link:- https://www.innerbody.com/image_digeov/dige10-new3.html#full-description