What advantage is their in having eggs with a leather shell?

the advantage of having a leather shell:

-protects the egg

-Some leathery eggs also have calcium carbonate but much more protein than the average bird egg. This protein is typically keratin, which is the same type of protein that makes up human hair and fingernails.

-Leathery eggshells do not necessarily have calcium carbonate. Some types of eggshells have little or no calcium in them at all, and instead are composed primarily of proteins. They may have other substances, such as lipids or some other mineral, as part of their makeup to ensure a solid, flexible shell.

-Tough, leathery eggs are generally very similar to hard eggs in structure, but the shell has some differences in its composition. Specifically, hard-shelled bird eggs tend to be a mix of calcium carbonate and protein. The protein helps make the shell smooth and holds it together, while the calcium carbonate gives it its hardness.

Biology