Based on this post in another thread:
Given the number of places that don't accept Amex what, in this day and age, is the appeal of Amex? Why would anyone prefer to use Amex rather than Visa or Mastercard branded cards?
The clue is in the name “American” Express.
its a card just about every professional working American has, and most corporations of any size use. Its a card for globe trotting Americans, that citizens in other countries can take advantage of.
Places that accept Amex globally tend to benefit, from additional US customer business, and US travellers benefit its services especially as Amex has global offices and a network worldwide.
I once was in Bangkok, Amex called me, asked if I had been to a restaurant in Houston 4 hours ago, which, obviously I wasnt, and the card account laughingly knew it too. He said the fraud had been detected and a new card was already available to collect, or courier to my hotel, it was delivered to my hotel before I went to bed that night, they even spoke with my hotel to transfer the authorisation, and the airlines for my tickets for check in (“enter your card used for booking” etc).
If you travel beyond the UK, you can rely on Amex to keep you moving, even if in your own country it may seem less beneficial than other cards. Its value to UK customers, who only use it in the UK is more limited, but go abroad it will help you in trouble more than your other cards will. They also err on your side first in a dispute. They have much more back up and advice options than other cards, for example I once used it for a suitable Business Restaurant reservations in Manila, (not knowing the place that well), and making the booking and arranging your car from your hotel..
Amex is good for lounge access, flight, car and hotel upgrades and certain rental car insurance cover too.
No British bank can offer that kind of service, maybe HSBC, tbh only a few US banks can match it for that matter (Citi, JPMC, Morgans perhaps..) . Lose your card abroad, your stuffed for a while if you didnt go prepared.
neither Visa nor Mastercard are issuing agents with global branches to offer that kind of service either.
What I say though, is Amex Travellers Cheques are next to useless, especially in the US. Last tried using them 20 years ago, and they were already useless then.