If you play modern video games, you know that the difference between the bottom and top frame rate can be very large. If the frame rate is much higher than the monitor’s refresh rate, which is usually 60 Hz and corresponds to 60 fps, you can see image tearing artifacts. It’s when the top and bottom parts of the image appear to be torn apart.
This problem can be eliminated by means of vertical synchronization. However, the solution causes another problem. If the frame rate is lower than the monitor’s refresh rate, the enabled V-Sync lowers the effective frame rate to multiples of 60 Hz, i.e. 30, 20 or even 15 fps. That’s not comfortable to play.
So, the point of adaptive V-Sync is in turning on vertical synchronization when it's necessary (i.e. when the game's frame rate is higher than the monitor's refresh rate) and turning it off when it's not necessary (for example, if the game’s frame rate is 50 fps, i.e. below the monitor’s refresh rate, vertical synchronization is turned off to prevent the frame rate from plummeting to 30 fps).