So…what exactly is v-sync? 
It’s short for vertical sync, where the flipping of a double-buffered fullscreen window (or regular window) is synchronized with the refresh rate of the monitor. This way it only flips the back buffer to the front at the start of the monitor redraw. If you don’t do this, you get screen tear, where the top half of the monitor draws the old front buffer, and the bottom half displays the contents of the new front buffer (which is usually 1 frame ahead so animations look off).
Thanks! Is v-sync enabled using BufferStrategy?
But is that really really noticeable ? I’ve been working with LWJGL for a few months now and I have Vsync disabled since then , and I could never notice this effect you described .
Two things. IMHO screen tearing is less noticeable on LCDs in comparison with CRTs. Perhaps due to the lack of a (real) retrace (the motion of the “gun” painting the physical pixels). The previous is just my opinion. The second thing is that tearing will be more or less noticeable depending on the properties of the two frames being displayed at the same time. The larger the “gap” in the two images and the higher the frequency will cause it to be more apparent. As an example, a first person shooter while the player is turning.