Working in a service profession in which we do many things that are invisible to the public (unless they don't get done!), I may have a bit of a bias. I have had repeated great service from the concierge at CDG (cannot recall her name at the moment) including help when my teen niece who was supposed to be on our flight missed her connection and had to fly solo on a later flight; EWR concierge for the PKG flight (Walter, IIRC) was incredibly efficient and helpful; HKK not only did the laminating thing with a business card but actually followed up with a greeting card on my next birthday. Have seen Concierge on other routes (most recently EZE) help resolve things like travel companions in scattered seats, handling things in a calm, professional manner.
Given the gazillion things that can go wrong and affect service quality on any given flight, I'm glad they are there and suspect they do a lot behind the scenes as well as in the aisles before takeoff.