Many consumers keep old, unused credit card accounts open to boost their credit scores.  Old accounts often help your score by extending the length of your credit history as well as improving your credit to debt ratio.

However, credit card companies routinely close accounts that show no activity at all. When an account is involuntarily closed, it changes your credit to debt ratio (or utilization rate), negatively affecting your credit score. In addition, your credit report will also contain an entry noting that the account was closed by the issuer. Many lenders view this negatively and may perceive you as a credit risk.

To safeguard your credit score make sure to use your old credit cards occasionally.

 As reported by the Wall Street Journal:
Credit Card Issuers Cut Off Consumers