There are different cost benefits for different category rewards, some are more cost effective than others. That has been analyzed here before. For some category levels or seasons, the cost difference is less. The point of the miles can be this - I am short say 90k United miles to get to Australia. I can simply burn the Bonvoy points to get the amount I am short. We have flown to Australia many times, for $0, both wife and I. So, they can be used to supplement any existing shortage. Category 8 is more than 80k, standard rate is 85k, peak rate is 100k/night, so at peak rate, the math becomes 150k difference for 100k Delta miles. The difference for a cat5 is 170k at standard rate, only 150k at peak rate. Used by night as your example shows, the benefit is different depending on which season. Unlike the per night rates which are based on season, a certificate is good for peak rates. Also, United is 110k miles. Valuing Bonvoy points as the points guy does, 110k United miles are worth $1,430. The 150k Bonvoy points it costs are worth $1,200. Not a bad deal.
