The idea of punishing a puppy makes no more sense than the idea of punishing an infant child. Have you ever heard of anyone spanking a baby? The only thing that would do is make the baby cry, and make the adult feel badly. A small baby wont learn from punishment, and puppies are no different. Just like everything you do with a small baby is designed to let it feel loved, protected and close to you, the way your treat a new puppy can affect the way that dog views you for entire relationship.
If you choose to punish a puppy, the most you will do is scare it and make it wary of you. If you smack a puppy, even lightly, all it knows is the pain of the strike and the fear it feels at that moment toward you. It doesnt learn that it was doing something wrong because its too young to understand that concept.
If your puppy is chewing on something for instance, and you punish it with even a light tap, of course it will probably stop what its doing. Its surprised and possibly feels pain from the smack, and now feels very frightened of you. It doesnt link the punishment with what it was doing, though, and has no way of predicting when it might be punished next....