Vertical Synchronization may show up as V-Sync on some game menu options. Turning on vertical synch will give a much smoother look as you turn left/right. If it's turned off, you will see tearing, where the image isn't quite stitched together.
It's really a personal preference whether to turn it on or not. I personally like having V-sync on because I don't like the tearing effect and it is much smoother on my eyes. Others like having it off because they want the ability to have a super high FPS count.