Debit and credit cards can be a big business for the companies that issue them. Citigroup (NYSE: C) and JPMorgan Chase (NYSE: JPM), the undisputed leaders by outstanding credit card loans and number of active credit card accounts, would prefer that Americans whip out their credit cards as their default payment method.

According to data from the Federal Reserve, whether we use debit or credit is largely a function of how much we're spending. When we buy something small like a coffee or a candy bar, debit wins out. But when we spend big on purchases such as flights or supplies to build a backyard deck, credit reigns supreme.

Why Americans use credit for big purchases

There are completely logical reasons for why we prefer credit for larger purchases. Credit cards aren't just a way to pay, but also a way to finance a purchase, so it only makes sense they get priority over debit cards for the subset of purchases consumers want to finance.

Many of the things that cost the most -- travel, restaurants and entertainment -- are most rewarding to put on credit, thanks to how many rewards programs are designed. JPMorgan encourages credit spend on travel with its travel-focused rewards cards. Citigroup has similar travel rewards cards in its portfolio, but it also gets a big share of large transactions thanks to its special deal with Costco, which put its cards in the hands of Costco's higher-income, higher-spending clientele.

Then there is the issue of fraud protection and charge-backs. Credit cards are safer to use than debit cards if your account information gets in the wrong hands. And most corporate spenders -- American Express's (NYSE: AXP) bread-and-butter business that JPMorgan Chase is increasingly fighting for -- have company credit cards, not debit cards. Strike another win for the credit category in large transactions.

All this is to say that there is a long list of powerful financial incentives that steer consumers toward credit cards for larger purchases. Consumers are simply acting in their best interest by using credit cards for a greater share of the dollar volume of larger transactions.

What's in it for the banks?

Whether you pay by debit or credit really matters to the banking industry, which collects fees on every swipe from cards they issue.

How the payments industry collects its share of fees, and how the proceeds are split between parties, is seemingly purposefully complex. But it is safe to say that most merchants (big-box stores, for example) would almost always prefer debit to credit purchases. Banks that issue the cards want you to pay by credit.