As per the patent description, this fingerprint-scanning display is able to register up to four separate prints simultaneously. This is courtesy of a thin fingerprint-sensing layer, rich in sensors, positioned either below or over the display of the device. In the end, Apple claims that its tech could evolve into a "a full panel fingerprint sensor".
It seems that the user will be able to "simply press a finger onto an icon placed on the display for scanning related to a user's ID". This hints us at some new plausible functionalities - for example, users might be given the ability to launch a certain app with their fingerprints only, thus preventing others from opening it. But of course, we're just speculating here.
We should not rule out the possibility that Cupertino is just making sure that it will have the upper hand if someone else comes up with a similar idea.