Yep, even if the credit card didn't offer any rewards or protection, I would still use them because I'm billed a nonzero number of days after the charge happens. And that's an interest free loan, where I can instead earn interest. If your credit card balance is $5000, and you only have to pay it an average of 30 days after the purchases are made, well... The 30 day T-bill rate is currently 4.38%, so putting that $5000 into the safest, most liquid investment available for 30 days will yield $18.25, which is much better than cash or a debit card where you are immediately charged.