Screensavers were originally a way to prevent burn-in on older CRT monitors. The now-classic moving images in early operating systems were created to keep any single pixel on the screen from remaining in place for too long, leaving behind a ghost on the display. Modern screens like the OLED ones on Samsung's Galaxy S8 can also suffer from burn-in. Since the new flagship's Home button is virtual now, the company had to do something to prevent it from getting burned in to your display. The solution? Moving the Home button image around a little bit.
This subtle movement can only be seen with careful measurement but it's definitely changing position by a pixel or two, notes Dutch site Galaxy Club. The feature was confirmed in an exchange between a Samsung superfan and the company's official Dutch Twitter account, as well.
@Samsung_NL Ques: "verspringt" de "Home-button" ook als je S8+ AOD aan hebt staan (zoals de andere info WEL verspringt), of...?
— henklbr™ 🇳🇱 (@henklbr) April 24, 2017
Smartphone screens aren't the only modern displays to deal with burn-in, either. LCD and Plasma screens can suffer from it, too. In fact, Android Wear devices that use OLED screens have a special anti-burn-in mode you can enable if you like to keep your smartwatch on all the time.