Some parents like to hold their baby up in the air, and it's okey. But others like to literally toss the baby and than catch them. It is a very dangerous thing to do!
Apart from adrenaline rush that it causes, it is harmful in other ways, too:
1) There is always a chance you won't catch the baby. Unfortunately, it happens too often, though people tend to think that it's never going to happen to them.
2) Free fall is bad for baby's neck - it's muscles are not strong enough yet.
3) This kind of "exercise" may cause damage to bones, brain and eyes.
It is important to hold baby's head all the time you play with them. You can lift and hold the baby, but never toss it up in the air!