Is marriage necessary or important?

I think it is good idea to live together before marriage because couple can see each other's life style and get used to it. I heard that in many cases, the relationship between couple or friend get worse as living together even they are really good friend or couple. It is because their life style is different as living  different family so there might be something they won't like. When they started see bad points as living together, some might brake up. So I think it is good to stay together and it is not necessary to get marriage if they do not want to because it is their comfortable style to be together. But still, sometime it is hard to have children if the couple didn't get marriage. Maybe, children will get confused, so it is not necessary or something important but good to be family.