I have had the two extremes with chat this week...
One where I simply wanted to get added to the C+ upgrade list during check-in window (I was in exit row Main due to late booking when C+ was full, but seats had opened up). Agent managed to reassign us to row 34 and lose our exit row seats and still not add us to the C+ upgrade list. Said "sorry I understand your frustration, but it is now under gate control" (21 hours before departure).

Later, while in a meeting I used chat to successfully book a couple of 80,000 SM business class tix from Europe to Asia on AF which kept erroring out online. Agent did it in about 5 minutes, and got seat assignments on AF to stick over 6 months in advance.

The ultimate YMMV situation.