When money is cheap, there's only one reason to lease a car instead of buying it.

It's the same reason people turn in their smartphones every two years.

You'd think that post-recession drivers would want to avoid financing and debt, but that hasn't been the case with car buyers at all. The Federal Reserve Bank of New York notes that U.S. auto loan debt stood at $1.1 trillion in June. That's $97 billion more than it was a year ago and is the second-fastest-growing portion of consumer debt behind only the $246 billion increase in mortgage debt from 2015 that brought the nation's mortgage tab to $8.36 trillion.

Auto loan debt is within a hair of U.S. student loan debt ($1.26 trillion) and is nearly $400 billion more than the nation's $726 billion credit card debt. While 3.5% of auto loans that are past due, that's nothing when compared to the 7.2% of credit card debt and 11.1% of student loan debt that's similarly in arrears.

Unfortunately, that default rate exceeds the 1.8% of mortgages that are behind on their payments and is up from 3.2% in 2014 and just 2.2% in pre-recession 2006. It's also worrisome that 22% of all car loans fall into the "subprime" category of borrowers with credit scores of 620 or less.

"Growth rates continue at unsustainable levels," says Nick Clements, former banker turned consumer advocate and founder of personal finance advice site MagnifyMoney. "Too much risk is being taken, and defaults will be coming."

Even new auto loans at credit unions a have jumped 15.7% within the last year, accounting for 18.4% of total loan growth, increasing $20.7 billion year-over-year and adding 572,550 new auto loans the national total, according to credit union analysts Callahan & Associates. Used car loans, meanwhile, rose 13.4% since August of last year, account for 25.8% of all loan growth during that span and have an average balance of $11,941.

David Walters, certified financial planner and certified public accountant with Palisades Hudson Financial Group, notes that drivers who plan on staying with the same car long-term have only one real option.

"The longer you own your car, the more you'll save buying versus leasing," he says.

A recent report by personal finance site WalletHub discovered that automakers' finance arms charged 1.45% on average for 36-month car loans from July through September versus a 4.58% annual percentage rate for leases. If you have your eye on a Mini, for example, the 0% finance rate for loans turns into a 7.8% APR if you decide to lease. Want a Dodge? A 2.9% finance rate jumps to an industry-high 10% APR for leases. Even Mercedes-Benz, Audi and BMW lease rates didn't exceed 5%.

Walters also argues that buying gives you more control. You can sell or trade in your car whenever you like and, if you own a car outright, there are no restrictions on how you can use your cash. You also don't have to worry about excess mileage or wear and tear.

"Buying a car also frees you from worry about incidents that can trigger fees in a lease," Walters says. "Leases have penalties for excess mileage and for wear and tear. And if you want to customize your car, you can."

Though Walters suggests that buying is a better deal because the diminishing rate of depreciation makes it cost less to own an older car than a newer one, this brings us to the one good reason to lease: updating. When a lease ends in two to four years, lessees typically move on to another lease. Models update, features are enhanced and the terms of a lease still require less of a down payment than the 10% to 20% that financed purchases require up front. In some cases, the dealer will waive it altogether.

Meanwhile the cost of buying also includes higher monthly payments that result from paying the entire purchase price as well as interest and finance charges. With a lease, you don't pay the cost of the car, but that of the depreciation. Also, when you're done with the vehicle, you don't have to worry about the price you'll get for it. If you manage to end your lease without going over your mileage limit or missing routine maintenance, there's a good chance you'll score a better deal on your next lease.

"If you'll definitely want a new car in a few years, you may end up paying enough in finance charges that leasing is the more logical option," Walters says.

That said, you're sacrificing flexibility and equity. You can't end a lease early without paying early termination fees that are as much, if not more, than the cost of completing the lease. Even if you manage to avoid mileage penalties for going over the typical 12,000- to 15,000-mile-per-year limit, there's a chance that the dealer may not find the wear that your pets and kid put on a car nearly as "normal" as you do.

Then there's the small issue that you're always going to need excellent credit to get a lease. Granted Overall, buyers who have fair credit will spend $6,671 in additional interest payments over the life of a $20,000, five-year loan than their counterparts with excellent credit, but at least they can get a loan.

At any rate, it always makes sense to haggle. Walters notes that you'll get a better deal if you negotiate as if you plan to buy the car, even if you decide to lease. That way, you'll get a decent price and some additional trade-in value for your trouble.

"Match your decision to your needs, finances and lifestyle to minimize the cost of owning cars over the long term," he says.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.