I assume the app and the retailers knowing everything about you, just like has been the case with loyalty cards forever. A degree of buy-in: you’ll go to the place that uses the app because it’s more convenient. Easier to spend money when it’s just a swipe on the phone rather than handing over cash - of course, credit cards have had the same issue for decades.
I wonder if there’s some sort of Uber effect, where these apps come in, are priced too low, make the market uncompetitive and wipe out everyone else, and then you’re left with a blighted landscape. But that’s idle musing: I don’t recall reading anything to that effect for mobile payments.
I guess it could lead to weird side-effects like what I encountered in China with some students last year, where we all relied on the one student from China because her phone could do basic things (order a taxi, pay for a meal, book a restaurant) that none of us could do because those things are no longer routinely done by voice calls or credit card.