No. Letting babies cry doesn't do a thing for their lungs.
Babies cry for a reason, although sometimes it's hard for adults to figure out what that reason is. They may be hungry, tired, wet, or overstimulated. They may need to vent, suck, or simply be comforted.
Crying doesn't benefit babies physically or emotionally, and it doesn't teach them to cry less. In fact, studies show that babies whose cries are responded to cry 70 percent less than those who are ignored.
Article taken from www.babycenter.com
I'm sure you've heard someone older say it, that its okay to for the baby to cry because its exercise for their lungs. But thank goodness for the internet to help us debunk so many myths!