Where does the cash come from? I assume you keep the money in some type of investment like stocks until you can afford the new car? Not a horrible idea, but not necessarily the best idea either.
Any annual return you are getting on your money is lost when you pull it out to pay for the car (obviously). So say you are getting 10% APR on your money in the stock market. Then you sell off your stocks to pay for the car, to save having a 6% loan.
Had you just gotten the car at the beginning, with the 6% loan, you could keep your money in the market earning 10% APR, and using the profits to pay the 6% loan. This leaves you with an extra 4%APR. And, you got your fancy new car when you first wanted it, rather then having to wait!