What are the actual benefits of marriage and how do they outweigh the risks?

If you love somebody and want to spend the rest of your life with them, why sign the piece of paper and accept all the legal baggage and potential for financial devastation rather than just living with them? I mean, an ex girlfriend can hurt you pretty bad, but she can't f*ck you up nearly as bad as a ex wife. Really, what's the difference between being married and living with a woman and raising a family with her WITHOUT the piece of paper?