As a rule, I always pay my credit card bills in full and on time. I just don't see the point of paying those high interest rates and those penalty fees. Even so, I think I have spent more money than I should have had ever since I got myself a couple of credit cards, simply because it's so easy to spend money when you don't have to actually count out the bills.
And there are cards that credit you back a certain percentage of your spendings, varies from 1% to 5%, depending on what kind of card you have and where you spend it. I've got unavoidable bills I've got to pay each month, like the apartment's maintenance fees, phone bills, utilities, etc. It's nice to pay them via these credit cards, at least you get some money back. Plus, when you buy a new car or a house, 1% of those kinds of purchases is some serious money.