While I almost completely agree with you, there is one exception... If you're applying for new credit, your FICO score will be slightly higher (I think 5-10 points) if your most recent balance reported is between 0% and 10%, but greater than $0.

Note this does NOT mean you have to pay interest because what's reported is the balance at whatever the end of the period is, so you still can pay it off completely (just not early).

The reason for this is because someone having a credit card and not using it has a slightly higher risk of default on new loans than someone who is using their credit card. Because the score has no memory of the balance of period months (only that it's been payed as agreed), and only the end of month balance is reported is why this works. The credit agency has no idea what your balance was in previous months, or whether you pay it off every month. They only know the most recent reported balance.

This also means that you do not have to use the credit card at all build long term credit, as it will show pays as agreed and the skinny week get older and older. But many credit card companies will cancel your card if you never use it to purchase anything (even if you pay it off every month, they still make transaction fees on each purchase).