I may get flamed for this, but carrying a balance once in a while to give a consumer confidence on a large unexpected consumer purchase that is a very good unexpected deal, is not always the worst thing in the world.

The trick is to do this :
1-low interest reward card.
2-An ethical issuer that uses average daily balance and not predatory double billing cycle method.
3-CEASE using that card until balance is paid off.
4- Actually pay of ENTIRE amount in 2-4 months.

Psychologically, I prefer to pay my C.C. bills out of transactional checking account.

I don't want to dip into my investment funds or emergency liquidity for bill payments.

Not all FT'ers are on a set stable salary.

Small business and self employed persons have fluctuations in income.
Carrying a balance short term is not necessarily indicative of living beyond one's means.

For those not on a set salary who have liquid assets earning 6%, then paying 9.9% is an effective interest rate of 3.9%.

If I clear the full balance it in less than 4 months , then I have paid a whopping 1%.

I'm willing to "lose 1%" for psychological comfort.
note #4 is the most important aspect here:
4- Actually pay of ENTIRE amount in 2-4 months.

Most consumers who carry a balance do so perennially and continue to use the card. You lose any and all grace period on new purchases once you have a balance.