You would be well advised to keep your accounts in a positive balance, stay in the black rather than the red, having your own money, rather than owing the bank money because you have a negative balance and are overdrawn. If you have a negative balance on your checking account for a long and sustained period of time, then the bank is within their rights to send your account to a collections' agency in an attempt to retrieve the amount of money owed. And this will really damage your credit score.