When a baby is born they have fluid in their lungs which is normal but needs to be removed once the baby is born so that the baby can breathe properly after birth.
Inside the womb the baby doesn't breathe like they do when they are outside the womb.
When a baby is born normal and healthy they will usually cry after birth which is always a good thing and a good sign that the baby has been born healthy.
The baby cries to get the fluid out of his or her lungs which means they are breathing properly and doctors would slap the babies feet or pat them on the back to get them crying.
The crying helps the babies lungs to clear out the fluid and get their lungs working properly.
So doctors do encourage babies to cry after birth.