Some eggs, I heard, have loose membranes. Now to explain that. An egg has the shell and a membrane and then another membrane between that one and the egg itself. Trapped between the two membranes is the air cell. *I don't even know how that is possible but lol* These membranes stick together and during shipping they can slip allowing the air pocket to move around. Letting the eggs settle for 24 hours generally helps restore that air cell to its proper place. While putting them straight into the bator with a rocking egg turner can keep the air cell loose and moving around. I really don't see how this can be an issue but it did make sense to me. Preserve the air cell in its proper location to insure a live chick.
The gal that told me this, always has great hatches from shipped eggs.
Arklady