“The idea that credit cards make you spend more does not apply if you have financial discipline.”
Unfortunately, this is not entirely true. A number of studies of consumer behavior with rewards cards were done a few years ago. They found that, in general, even the people who believed they were very financially disciplined and never spent on unnecessary items actually spent more than they would have paying only with cash.
It’s because in the back (or front) of your mind is always the thought that you are getting a reward for spending, not matter how disciplined you think you might be.
I use rewards cards extensively and I am sure they are saving me money but I am also certain I occasionally spend unnecessarily because of the rewards. The rewards I have received are quite large and probably have more than made-up for the unnecessary spending, but it’s still something there.
Probably the main reason I benefit is that I am able to place necessary spending like health insurance, auto and renters insurance, cable, internet, phone, cellphone and other bills on a rewards card (currently 3%). Amex occasionally gives 10% back on some of these things so I am getting 10% back on my cable bill for a few months right now. I also get 6% back on groceries (including prescriptions) from the Amex card.