Recently played Metro 2033 and fast sync practically saved the experience.
Game is full screen only, no borderless window, no triple buffering. Full screen and vsync yes/no. Period. So I lock to 60 because fuck screen tearing but I got horrible, HORRIBLE micro-stutter like I've never experienced in my life. Remembered this thread, looked up how to turn on fast sync and it fixed everything. No more micro-stutter, no screen tearing, higher fps and less input lag. It's like a dream. Finding it hard to think of a reason not to have it enabled on every game going forward.