Take the Chase Freedom Unlimited card, for example. It ears 1.5% cash-back in the form of points. Those same points can also be transferred to airlines (as long as you have their premium card)

If you have 115,000 points, you can use them towards a $1,150 cash credit. On the other hand, those points can also be used to book a Singapore to Zürich flight in their brand new first class, which would ordinarily cost $6,000+. one-way

An even more pronounced example: with just 30,000 points (or what would be $300 in cash-back), transferred to United, you can book HKG-SYD (a 13h trip) in business class, which would ordinarily cost $3,000+ one-way.

Oh, I see, you mean credit cards. I was thinking miles accrued from flights and was confused, thanks.