If you are staying at Hyatts regularly then the answer is to use the cert at the first cat 4 you would otherwise have booked with points (ie the $ cost is above your valuation of 15k points). That way you saved yourself 15k points. If you use it at a cat 3 that would have been $1000/night and then pay 15k points for a cat 4 the next week, you cost yourself 3k points.