Answer:
The only advantage is you avoid any interest for financing any part of the purchase price. The belief that you can get a better price if you pay cash is false. The sales person loves to hear you say "I'm paying cash" because he knows there will be no financing problems. The sales managers reaction will be to avoid a deep discount in the price because his only profit will be in the price of the car. If you have a trade they can typically make money off of that as well as when you finance a car through the dealership they are paid by the finance company in a number of different ways.