As a frequent flyer you don't have to pay the change fees - which can add up if you need frequent changes. I nay old job I used it maybe once a year - but changed job 10 weeks ago and have changed 7 flights to date for a grand total of £12 - would have cost be close to £250 otherwise. Have also noticed they often waive small fare changes.
I had a situation last year where all flights in belfast got cancelled on the spot with Hurricane Ophelia. Suddenly 500 people in rebooking queue - Flightclub line sorted it in 2 minutes.
Also - last night a fellow passenger was telling us he had to change and go home a day early due to a hospitalised family member. The FlightClub agent spoke to supervisor and waived £168 flight difference. So there seems to be some flexibility for frequent flies.
I was skeptical at first when my travel plans never changed - now think it is invaluable when travelling weekly and plans often changing.