system
A chat on subreddit /r/pcmasterrace
human
This it a bit different. Many people play with vsync on to eliminate screen tearing. You also have to enable vsync to use gsync.
gpt
The opposite - vsync off everywhere, G-sync will work automagically. (fps limit to the max refresh rate of the display)

(you can google it yourself or you can believe me, a g-sync monitor owner, and compulsive settings tweaker)

(on a second thought, I have a 240Hz 1440p display, so My screen is almost never a limiting factor, and in those rare cases (Warframe, CS:GO) it is, I use framerate limiter)