Credit Card Promotional Rates
I do not usually recommend using a credit card if you do not pay off the entire balance at the end of the month.
I do make this exception. If you have made the mistake of getting into long-term debt by means of a credit card, then you want to pay off that balance as fast as possible. One way to do this is to sign up for a zero-interest promotional rate card and use all of the borrowed money to pay down the balance on your regular credit card.
Promotional rates by law have to be for at least six months. Some cards offer an 18-month zero rate. These are ideal. You escape all interest for 18 months, and then use this money exclusively for the repayment of debt on a high-interest credit card.
Here's an article that discusses this strategy. it also discusses some of the pitfalls. You had better be aware of the pitfalls. Sometimes the zero rate is a disguised balloon payment loan. Avoid these.
This is a sensible use of credit card debt. I think it is the best use of credit card debt.