Interest payments on a depreciating asset. If you can figure out how much money you'd loose over the life of the vehicle and then make a rational decision that you can afford it great. If you taking out a car loan on a new vehicle that would then be a large percentage of your disposable income, not so great.
Debatable.
Interest is beyond negligible for most people with a 2%-3% rate, and most car loans these days are sub 1%.
Basically what you are saying is you'd buy a new car for $15,000 but not $15,800*. The difference is so little over the course of owning the car over many years that you won't even see it. Over the course of 10 years that $800 extra in interest payments is about
$7 a month. You will spend far more in oil changes than you will in interest.
In fact, if you read between the lines here, you're actually throwing money away writing a $15,000 check for that car vs. putting it in a fund that over the course of time will greatly eclipse that paltry 1-3%% APR you're paying on that loan.
While true a car is a depreciating asset, it's value is far beyond the actual number on paper and it has intrinsic value and is truly an investment. It provides transportation to get you to and from work where you make money (for most of us). Is a $10,000 non-running luxury car worth more than a $5,000 reliable beater? To me and most folks it is.
Buying a $40,000 car on payments vs. a more reasonable one just because you can afford it is a different story, but for those who do not work on their own cars and downtime is precious, time at shops are lost days at work or a $40 taxi ride to and from make that extra $7 a month seem penny wise and pound foolish. I have bought several broken down cars from folks who did not have the time or resources (money) to fix them and whose choice was take a roll of the dice on another used one or get back on their feet with a brand new car for less than they were spending keeping their current one going. Couple that with the fact that used cars these days are not anywhere near "cheap" in relative comparison to a new one, and the case can easily be made for a new one.
* $15,000 new purchase price, 4 year loan, 2.5% APR keeping the car for 10 years.