Concorde shaved about three hours off the trip between NYC and Paris or London. It burned ungodly amounts of fuel (two tons of fuel just taxiing to the runway), cost a ton, didn't have enough range for Pacific routes, couldn't fly transcontinental routes because of the sonic boom, and after all of that it only saved a few hours.
Of course, Concorde is old technology and it could be done a lot better now. But you'd still be saving a limited amount of time (roughly a factor of 2), burn more fuel, and be more limited in range compared to a traditional airliner.
BFR would have enough range to connect any two points on Earth. It would have no restrictions on overflight (although it would most definitely have restrictions on where it could launch and land). And it would save 10-20 hours over a direct subsonic flight.
Cost? Well, I don't know. Elon says it'll be pretty cheap, but I'm skeptical. However, given how much more capable it would be than a supersonic airliner, it might be worth a much greater cost. Part of the problem with Concorde is that it just didn't save that much time.