They're useful when traveling for work. Not because they can find you better deals (they rarely do), but because they can save you time. You can book a flight, train, hotel and even tickets to the game/show you want to take a customer to with a single call and get all costs on a single invoice sent in the correct format, to the correct address with the correct fields filled in for the invoicing system. There is also a single 24 hour phone number to call if things go wrong where you can instantly talk to someone who can sort out whatever the problem is.
But as I said, none of this involves actually saving money
But as I said, none of this involves actually saving money