Why is the engine frame-rate limited?

[nofsky]

Kleetus, read Eigenmusic comment, in particular the first paragraph. Just because your framerate is 60 and your monitor is at 60 hz does not mean they are synchronized. The timing on both must match exactly or there may still be screen tearing. The frame limiter in the game may not be as exact or the fps may drop below 60 fps, thus making it out of sync. Screen tearing is when the game forces the monitor to begin updating the screen with a new frame before it is finished with the old. V-sync makes the timing exact by forcing the game to wait until the monitor is finished updating the screen.