For domestic flights, I often buy a b fare and upgrade. Yesterday I was plotting a domestic flight, and there was a new option: First/global first. For the flights I looked at, the price was materially lower than a b fare, and gave me an a fare.

I'm hardly complaining, but I'm wondering if there is some disadvantage to the First/global first option. There didn't seem to be any explanation on the web site of this change.