I believe the OP was noting that they finance items on a Same as Cash basis, paying off the balance before the due date of the SAC period.
I do this myself on all major purchases. I have the money already set aside and dedicated to paying off that debt in an interest-bearing account. I generally divide the purchase by the numbers of months minus two (so I always pay the balance two months prior to the promotional end date). So say my iMac 5K at 24 months at $4000, I pay $182 a month so the balance is paid in 22 months and I am earning interest over that period.
It's not hard, but there are benefits to me in using the CC and floating that balance in an interest-bearing account for the 20-30 days that I would not get if I paid cash up-front. Your mileage may vary.
Ahh, I didn't realize folks were talking about 0% interest credit cards. I've never tried to set up a purchase like that with a 24 month 0% interest period. It could certainly make me a bit of money doing it that way.