Why is the guitar inlaid with shells?

Guitars of the same brand and series are classified according to different grades. It's not just decoration. Just like the difference between a three-star hotel and a five-star hotel is not just numbers.

For example, a piano body with a white edge is superior to an infinite one, a piano body with five edges is superior to an infinite one, a piano body with a shell edge is superior to an infinite one, and a piano body with a back center line is superior to an infinite one. This is a way to distinguish grades with the same brand. Without these technologies, all guitars of the same brand and series would be the same. (Of course, the corresponding methods are materials and workmanship. )