From my understanding, what is used is called an "opportunity cost". Meaning, if I took this loan rather than pay off the car, I now have $36,000 in my possession that I would not have otherwise. I have to be able to make more than %1.9 off the money I spent over seven years for that loan to have been worth it.
So let's say I just store $36,000 in a savings account that had a yield of less than %1.9 and used that to pay off the loan. I am still losing money on the deal. If I put it into some sort of investment that made more than %1.9, then I make more money than if I spent it entirely on the car.
This is at least my understanding of how it works out. I welcome other's thoughts if I am wrong.