In modern times the use of personal computer screen savers has changed with the advent of liquid crystal (LCD) and light emitting diode (LED) displays. Back in the day, however, in the early develoment of personal computing, the display screen technology used would literally burn an image of what’s on your screen into the screen itself if the image stayed constant for too long. This phosphor burn-in of, particularly, cathode ray tube (CRT) screens resulted in the advent of the screen saver industry.
By providing a constantly moving image for your CRT screen when not in direct use, screen savers prevented phosphor burn-in and extended the life of your then very expensive screen.