Having been hit for overdraft fees for resoling my shoes years ago, I can tell you that it's a big deal for someone living close to the line. Happily, I'm no longer in that situation and now the bank pays me 1.5% to 4.5% for spending money on its credit card. I still don't understand that, but there are no bank fees on me.
You're getting a kickback out of what the vendor pays your bank to process the purchase on their card.