G-sync dynamically adjusts refresh rate of the display (to match the frame rate), correct?
If your frame rate remains steady at 60 FPS, I'd argue it's not needed.
Maybe useful above 60 FPS, assuming the frame rate dips in some games.
Not quite, its little more than than that & you thoughts are little backwards.
without Variable sync tech
GPU generates 30-100FPS it will send the image directly to Monitor as soon as its ready, so could be getting 2 frames in 1 screen (screen tearing) normally spilt top/bottom
Even if you kept a steady 60fps you could still get screen tearing if monitor is responding to the frames it recieves slower than expected.
With variable sync tech
GPU & monitor communcate & keep in "sync" to display an entire frame when both the monitor & gpu are ready. (no screen tearing)
normally gpu sends frames to monitor & monitor will cache them ready (hats why gsync modules have memory)
Gsync/Freesync
Its most useful below 60fps as the technology will duplicate frames the gpu generates to provide a more smooth experience when at low fps, EG 30FPS from GPU will have 30 frames & 30 duplicated frames making it feel lot less jarring.
Again will also be affective at +60FPS creating no tearing vs GPu bpushing ot 300 frames that a monitor can not display in time.
So actaully Sync is better <60FPS & >= 60FPS
think of it as a factory production line.
GPU -> Monitor -> User
if not in sync GPU could "overload" the monitor thus creating bad qaulity control
in sync GPU will wait for monitor to be ready before it sends a frame - Better qaulity control
i had 11 total Gsync monitors and 5 Freesync monitors i would never game without one.