Making it legal

My fiancé and I have been engaged for over a year now and we haven't really started making marriage plans. We are happy with the way things are going and quite frankly a wedding is expensive. What are the legal benefits to being married? We live a pretty budgeted life and I don't know how putting our names together on paper will effect our taxes, credit, etc. I honestly don't mind either way I know some couples who have been together 20+ years without ever making it legal and others that seem to get married right away.