I have heard that when a bullet expands to twice its original diameter that is optimum bullet expansion. I have also heard that if the bullet stops on the opposite side of the animals hide then that is optimum bullet expansion.

I can understand the theory of double the diameter from a metallurgical stand point, and I can kind of understand wanting the bullet to stop just at the hide on the opposite side of the animal. But neither of these explain optimum bullet expansion to me. I think of optimum bullet expansion more of how the bullet will open as it penetrate the animal. I don't want a lot of bruised and pulverized meat in the shoulder, but I do want the heart and lungs to be pulverized. Any input? Should I care about an exit wound or not?