Socialization can mean so things depending on who you ask. To me, socialization means proper exposure to new smells, animals, environments, textures, sounds, and many other things. Rather than just flooding the dog and making them shut down, I like to use positive reinforcement to encourage dogs to be more confident and comfortable getting outside of their shell. Socialization increases your dogs confidence by showing them that they can get through and over scary overwhelming things, this can also help teach them how to react in uncomfortable situations. This is very important to help prevent your dog from being very fearful which can lead to reactivity, fear aggression and other issues. It's also important to remember that it's not all in how you raise them and genetics matter, not every dog is confident and not every dog will want to be around others but neutrality is the goal. 

Proper dog on dog socialization is also extremely important in helping dogs understand pack dynamics and other social behaviors. A lot of dogs really benefit off of interacting and playing with one another.  You don't just throw dogs together and let them figure it out, I always make sure to closely monitor body language to make sure everyone is comfortable. 1 bad experience can really ruin some dogs so it's important to always watch what dogs your letting your interact with yours. Dog parks are very dangerous for this reason. You want your dog to associate being with others as a positive thing, not an overwhelming experience when they fear for their safety.