Remember Flying Toasters? Yeah, it’s kind of like that.
Screensavers were originally a way to prevent burn-in on older CRT monitors. 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.
For that the company moved 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.
Smartphone screens aren’t the only modern displays to deal with burn-in, either. LCD and Plasma screens can suffer from it, too.