You turn vsync OFF, actually!
Vsync synchronizes the number of frames your game will produce to the refresh rate of your monitor. Gsync (and Freesync) allows for variable framerate meaning you don't get tearing no matter how many frames the game will spit out. You cap it, so that it won't overwork itself making more frames than the display can show.
You can think of vsync as in synchronizing your game to follow the capabilities of your monitor. Gsync/Freesync on the other hand, makes the monitor follow the capabilities of your game (or GPU).
Now here's a caveat: that's how I understand it, and I could be totally wrong! If so, I've been doing my settings wrong for past 2 years. I'm too looking forward to other replies!