Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I think if you leave your screen on a specific "image" (say your desktop), there is a chance your screen is prone to getting "burned" with whichever colors are currently on screen. The screen saver has effects which keeps the screen never having to stay on a specific color or image which prevents burn in of colors.

(I hope that's clear...)

Anyone else can chime in, hopefully with a better explanation!
 
* A screensaver is a type of computer program initially designed to prevent "Phosphor burn-in" on CRT and plasma computer monitors by blanking the ...
en.wikipedia.org/wiki/Screensaver

* A computer program that displays aesthetic patterns or images when the computer is not being used

Use google
 
A screen saver could save a CRT or Plasma display, but it is not necessary for an LCD (or even most modern CRTs, for that matter). It is better to have the screen go off when you are not using it since that saves power and prevents any burn-in. I only use a screensaver on my Mac because that's the easiest way I know to lock the screen.
 
Thanks that made it more clear. I just work on my mac alot and its on for around 12 hours a day. I got one more question. If you dim the screen will it help saving the screen? I heard that the less you lower the brightness the better it is for the screen.

:)
 
Dimming will help a little. Light from the backlight will cause the colored filters in the LCD to fade over time (5-10 years), and redusing the brightness will prolong the life a bit. It might also extend the life of the backlight istelf, though that shouldn't be an issue with LED backlights since they should last around 50,000 hours (though a component in the backlight controller circuit will probably fail first).
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.