To say hello, of course. Puppies are social creatures and happy and excited to greet just about anyone! Jumping, leaping and bouncing are ways your dog shows affection and receives attention. When a puppy is very young, we usually sit on the floor, let them wiggle into our laps and allow them to lick and nuzzle up close to our face. This is OK because we are down at their level.

If you have ever seen two dogs when they meet, they greet each other face to face, unless there is a massive size disparity. So, why are we surprised when that is how a dog wants to greet us? You come home from work and let your dog out, and they are excited to see you and excited to show you how much they have missed you. So they jump up on you to get closer and give you some love. 
Homecomings and departures are a prime time for jumping up because puppies want to greet you or stop you from leaving. Turning your back on some of these dogs revs them up even more, so instead, try ignoring the bad behavior. “Ignore” means you make no eye contact, say nothing and stand still like a zombie offering no reaction to silly puppy behavior.
Understand the dog's behavior. In a dog's world, it is instinctual to greet another dog by coming nose-to-nose with them. This allows them to sniff each other's faces and become acquainted with the other dog's scent. Of course, your nose is a bit higher to reach so it is only natural that your dog will jump up to get closer to your face when greeting you.[1] This can be quite annoying and unnecessary, but fortunately, the habit can be broken.
Puppies should be told from day one, "no jumping." Anything you do not wish your cute little puppy to do when it is full-grown should not be allowed when it is a puppy. Think about the behaviors you allow your puppy to do; is it something you will always allow him to do even when he is full-grown? If the answer is no, do not allow your puppy to do it from day one.