When you're going to have kids it's a good idea to give the children a stable family life and the same last name.

When you're not having children some marry to receive benefits like health insurance and division of money.

My own feeling is if your not having kids, I wouldn't recommend it. Divorce at any age is extremely stressful and where money is concerned, hey I'm not sharing mine if we are no longer living together. It's just easier to walk out without a certificate. I don't like feeling stuck or like I have to take care of you because we are married. People and circumstances change over the years and I'd rather freely choose to stay or go (and for my sig. other to do the same).