gap coverage is best gotten thru your auto insurance agency. you can take it off at anytime that way. if you get it thru the dealer, they charge you for coverage for the full term up front, then add it onto the loan.
as far as financing.. some of us feel greater need to have a reliable vehicle. if it were just for me, i’d buy a beater for cash, but having wife and kids, i feel more comfortable with a car with a warranty, that i know is going to start every time i stick my key in it.
It's usually about $200 for the life of the loan.
For my family, it's important because the cars we buy are good quality but suffer from rapid depreciation (think Mitsubishi or Hyundai here).