Presumably, if one could expand his rib cage farther, he could breath deeper...
Pearl Divers and Sherpas are both said to have "Thick Barreled Chests".
Is this observation reliable?
Is the huge ribcage a result of Free Diving for Pearls or Carrying Large Loads at High Altitude?
Or do these fields of endeavor simply select for those who already have that characteristic?
Actually though, until I read the question, I took it as an Unexamined Primary, that everyone would want a bigger chest, were it possible.