When determining your FICO score, they look at total balances in relation to your total available credit on revolving accounts. It's favorable if you have a good deal of available credit in relation to what you owe. Maxing out on various credit cards can indicate that a person is overextended, and is more likely to make some payments late or not at all. This will lower your credit score.

If you have credit cards that are paid off and you never use them, it's a bad move to close the accounts. You want that available credit to offset what you owe on your other cards.