While that is part of the benefit, the real benefit is that the refresh rate can always match the frame rate, making slight drops virtually unnoticeable, because there will never be any need for duplicate frames.
It's simple math; if you have triple buffering on, with a standard monitor, and your framerate drops from 60fps down to say, 53 fps, there is going to be some stutter. Triple buffering will prevent frame tearing, but 60 isn't divisible by 53, so 7 of those frames are going to have to be repeated twice, causing unstable frametimes as 7 of those frames will have twice the latency as the rest. With Gsync however, the refresh rate would simply drop to 53hz, preventing any duplicate frames, and maintaining stable frametimes.