Many applications involve several screens of data that a user might want to browse or flip through to view each screen. As an example, think of an application where we list a catalogue of books with each book in the catalogue appearing on a single screen. A book's screen contains an image, title, and description, as in the following screenshot:
To view each book's information, the user needs to move to each book's screen. We could put a next button and a previous button on the screen, but a more natural action is for the user to use their thumb or finger to swipe the screen from one edge of the display to the other and have the screen with the next book's information slide into place, as represented in the following screenshots:
This creates a very natural navigation experience, and is honestly a more fun way to navigate through an application than using buttons.