The purpose why some of my friends have credit cards is they look after the reward system. They will just save the reward points and redeem it once they have enough reward points to pay for the things they wanted to purchase.
As long as the credit card user knows how to use it properly then using a credit card is an advantage.
I too use it for the same reason. I pay almost everything by my credit card and accumulate points. But I make sureI spend only that much that I have in my account to pay. Last year I bought a laptop where I could pay 75% of the anount on my accumulated points of 4 years. That was definitely a deal.