Here’s the answer from David Migoya at The Denver Post…
“One would think that’s a practical approach (not using it), especially if a card’s interest rate shoots up.
But there’s actually a downside to what might have once been acceptable. Though there’s no impact to your credit score for not using your available credit, credit-card issuers more and more are monitoring usage practices.
Non-use of a credit card is viewed dimly by issuers, who in turn either raise the interest rate in an effort to push you to cancel or simply cancel the account for inactivity.
Best practice: Keep dormant cards active with a small purchase every couple of months and pay it off immediately.”
I’ve heard from several people that many card issuers are charging a monthly fee if there has been no activity. Be sure to check your statements every month, whether you use your card or not!