Does increasing this parameter make it match the screen better, or does lowering it improve the match?
0 means no visual latency.
When Screen latency is at 0, the effects will always be a little late (of course if your PC can run it at 120 fps it will be barely noticable).
If the delay bothers you, set the Screen latency to 1 (that should be enough for most people). If the effects are still late, continue increasing this value till they are synchronized with the screen.