A credit score measures your creditworthiness, based on your track record with credit cards, loans and mortgages. Establishing a credit history and building your credit score sets the stage for renting an apartment, applying for a car loan and buying a house -- and, generally, the higher your score, the less expensive it is to borrow. So, even if you don't plan to regularly use an emergency credit card, having one will help you build credit with minimal effort.