Can somebody explain why G-sync/Freesync is so good?

[GatoDelFuego]

I'm looking to buy a new monitor, and I'm confused as to what makes these extra features worth it. Say I've got a 60hz monitor, and my game's running at 90fps. This would cause tearing! The solution to this would be v-sync or nvidia adaptive v-sync, but this causes some input lag from what I hear?

 

But, if I have a 144hz monitor, and my game runs at 90fps, what's the problem? Why would I need an extra peripheral to make my monitor run at 90hz instead of 144? Basically I could see how this feature helps when your fps is above the refresh rate, but not when it's below.

[Glenwing]

I'm looking to buy a new monitor, and I'm confused as to what makes these extra features worth it. Say I've got a 60hz monitor, and my game's running at 90fps. This would cause tearing! The solution to this would be v-sync or nvidia adaptive v-sync, but this causes some input lag from what I hear?

 

But, if I have a 144hz monitor, and my game runs at 90fps, what's the problem? Why would I need an extra peripheral to make my monitor run at 90hz instead of 144? Basically I could see how this feature helps when your fps is above the refresh rate, but not when it's below.

 

You can get tearing at any framerate if the GPU and monitor aren't synchronized, whether the framerate is above, below, or equal to the monitor's refresh rate. It's just most common when it's above.

 

Synchronization also make the image a bit smoother by eliminating stuttering which can occur when you're below the monitor's refresh rate. If you're only getting, say, 50fps on a 60Hz monitor, then most of the time the monitor has a new frame every time it refreshes but 10 out of 60 times it won't, and it will repeat the last image, creating a stutter as that image is displayed for twice as long as all the other ones.

[Samfisher]

G-Sync is incredibly useful when you go below your refresh rate into territory that isn't smooth playing, like 45fps for example.  It slows the refresh rate of the panel to match the FPS so it feels and looks smooth, as if running at 60hz for example.  This means you can crank the graphic settings higher and enjoy the same smoothness. @GatoDelFuego