If you don't pay your full statement balance, you could easily find yourself racking up credit card debt. Not only will you be charged interest on your balance, but if you don't meet the minimum payment, you could find yourself being charged late fees.
Not only will not paying your bill at the end of every statement cycle increase the amount of debt that you owe, but it can have a negative impact on your credit score. If you are trying to build yours up, you will want to avoid this at all costs.