LaborinjoRt :
I don't personaly like v-sync. Lets say you have a mega machine that outperforms most other pc's. If you turn vsync, you are locking fps at 30, or 60 fps at most, while you could play like 120-140 fps. Its frustrating
Well, that would be it's job....
As you know, there is only a certain ammount of images that a monitor can hande. For examle if you're using a monitor in 60Hz, it's 60 images/sec.
Any more than that, and images will be "half-loaded" in every iteration, and the screen will be torn up. Especially in a game if you move the view left or right, you'll se a horizontal break/tearing.
This happens also, when there a less fps than hz...
V-sync corrects that, by setting the FPS cap for the refresh rate of the monitor. You wouldn't see more any way...
Well, it you have a 144Hz monitor, Vsync will set that to 144 fps of course.
In case your video card generates less, vsync will hold the last complete image till the next one is ready, and there is a new iteration on your monitor. (which slowes your performance down a bit.. but it's worth it, belive me)
Freesync and G-Sync are the hardware solutions for that. They set the monitor's refresh rate according to the game fps.
My monitor handles Freesync between 40 and 60Hz. so if the game fps is in that range, it works, and sets the monitor to that refresh rate.
The driver should be (and as I see it is) smart enough to know how vsync and freesync(or even gsync is those cases) work together.
As of my tests. In the 40-60 range freesync works perfertly. Below 40 and over 60 vsync takes over.
Of course there are monitors that are waaaaay better at this... with ranges of 30 - 144 hz.
But even in my case it helps a lot. As I usually set az FPS cap at 60(wouldn't see more with this monitor), and I usually set the game to work well. Even reduce some settings if necessary, but they usually deliver 50-60 fps. And even if it falls down to 40 it works.
So to answer the original question, as of my tests with my monitor(and it's quite limited options in this case)...
Yes, you should turn on Vsync!
In your Freesync range it won't do a thing(won't slow down you computer or do shuttering), below and over that range solves tearing the old way.
Please know, this is not an official answer from the manufacturer, just my quick test with my LG 27UD68