The effect on the credit score should not be the only reason why you contemplate closing or not closing extra credit card accounts that you have. For people who already have a good credit score it is generally advised that you should not worry too much about extra credit card accounts that you might have open even though they are unused.
Theoretically speaking closing down credit card accounts will raise your balance to limit ratio which might affect your credit score negatively. When you close down a credit account it certainly appears that job that has increased substantially as the amount that you owe has increased in comparison to the total amount of credit limit available to you.
But as long as you have a good credit score a temporary setback in a credit score which may be minimal at best will still not affect your ability to get credit in the future. What you can simply to its put away the unused credit cards safely in a place so that they do not get accidentally used in the future and create clutter and confusion in your monthly payments of your regular credit cards.
For people who have a marginal credit score closing credit cards might become important as even a small change in the credit score might make their credit score dipped below a certain threshold that the lender has four approving borrowers for a loan. The reason that a person with a marginal credit score might consider closing down extra credit cards is if that person cannot resist the temptation of charging these credit accounts and getting himself more into debt. You should make a decision based on what is best for you for a debt free financial future and not just based it on the impact on your credit score.
Another factor that might affect a person with a poor credit history and with too many credit cards is something quite the opposite of what has been said earlier about a high debts to balance ratio in better than a low one. While having several credit card accounts will help in keeping the debt to balance ratio high certain lenders may consider giving you a further credit a problem as they might feel that in light of the problems that you have had in your dreaded history in the past you already have a lot of credit available to you and it will be a bigger risk for them to extend you a further line of credit since you are more likely to be unable to pay your debt in the future.