If the card you used for a balance transfer isn't useful anymore, you might wonder, "Should I cancel that card?" The answer for most people is that you should keep your card even after you've paid your balance in full or the 0% introductory period ends. Keeping the card open helps your credit score, so even if it's in a drawer collecting dust, it may still be helpful for your finances.
Consider canceling the card if it carries an annual fee, you're having trouble staying disciplined with your spending or the extra credit line is a liability to your debt plans.