Originally Posted by
makfan
The disadvantage, if I understand the fare rules correctly, is that you are only guaranteed coach class should there be a cancellation or delay that requires you to be rebooked onto alternate flights (this is what we commonly abbreviate IRROP, for irregular operations). There is not a lot of spare F inventory on the day of travel for handling rebooking or rerouting. You'll still get the 1.5 points for the flight, but not the bigger seat for you and your service companion.
BTW, a full F fare doesn't guarantee a seat in F during IROPS either--trust me it happened last month. If there aren't any FC seats left on the next flight, and you want to go, then Y it is. They do put you at the top of the upgrade list (and refund the differance in F and Y if you don't make it) but that's still no fun when it means 6 hrs in coach.