[floydnoel]

what would a banking app do that a bank website can't, exactly?

[akvadrako]

Many bank websites require bank apps or hardware tokens to login.

[qingcharles]

IIRC some finance apps either don't have web sites that can perform financial transaction, or are lacking a number of features of the mobile app. Cash App and Venmo used to be some of the worst offenders, but have improved in recent times.