This feature has saved me literally hours on the phone with a GS customer service rep every month. I often book complex iteneraries with seperate reservations including paid & reward (paying for my ticket and using miles for another). For example I just booked a 6 segment Europe vacation, paid business class for me, and for my wife a combination of X+R & I+ON. I knew exactly which flights, and exactly what the inventory and it still took about an hour on the phone to book. This would have been many many calls to try and do without the feature (so much so I would have likely given up and just used miles & flown a partner airline for both of us).

Not only does this information help me self serve, and drive purchase decisions (to buy or not to buy), but it also helps me with flight selection. When flying domestically I will often book a less convienient time for greater upgrade odds. I suspect this is in UA's best interest (i.e. I pay the same price for a less popular route).

This is something that I personally use every day, and losing it will be a real pain.