Your credit rating matters a great deal. A good credit rating means you'll pay less for everything you finance -- cars, credit card purchases, homes bought with mortgages. According to MyFico, for example, borrowing $300,000 would cost a person in the 620-639 range over $100,000 more than the person with a 760 credit score. In addition, a poor credit rating can make it difficult to work in certain industries, so it's good to establish and protect a good credit rating early on.