Back when CRT monitors reigned supreme, screensavers were necessary to counteract the effects of display burn-in. These days, there's less of a need for screensavers, but they remain a vestigial part ...
Way back when: People used screensavers to prevent "burn-in" on CRT monitors, where static images could permanently damage the screen. Screensavers like 3D Pipes animated the display during inactivity ...