Not really. Baby's first cry is essential for a baby's heart. However, any further crying is a baby's way of attracting attention - when he is hungry, uncomfortable, or just needs a cuddle. Research suggests that letting the baby cry without intervening may lead to the baby developing an inability to cope up with stress as he grows up. So no, crying is not training his lung capacity. However, ignoring a crying baby can have adverse effects.
Scientifically, not really. It's more of an expression if anything. As parents, we give them more attention when they cry so they express themselves through crying to get attention.
No, that sounds like an old wives tale.
i don't think so, no.