If you've bought something online, you've likely seen the option to pay in interest-free installments -- even for small purchases, like clothing. This is called "buy-now, pay-later" and it's become a lot more popular. The value of buy-now, pay-later programs has increased over 1000 percent in the last few years. We talk to an economist about why that is, and how these programs might impact personal finances and the economy as a whole.