Look sensitivity

Look Sensitivity is a gameplay setting present in every Halo FPS. The option allows a player to control the speed at which their character turns. Unlike other games, however, Halo only allows the player to change the sensitivity with one setting; other games tend to have different settings for the horizontal and vertical look speeds.

A higher sensitivity setting allows a player to turn around faster; a lower setting slows a player's look speed. Look Sensitivity should not be confused with actual movement; it only changes the speed at which a player changes direction, and has no effect on movement speed. It is typically recomended to use a higher look sensitivity, though this does make it harder to aim. New players should start with a lower sensitivity, and slowly raise it as they get better at the game.

Advantages of a high setting

 * You can turn around faster to engage threats. This is often a lifesaver in close quarters, as it's very common for enemies to come from the side or behind.
 * In Halo 2, due to its enormous auto-aim, sweep-sniping (the act of moving the reticule of the Sniper Rifle across an opponent's head to get an instant head shot) will benefit greatly from an increase in sensitivity. This trick also works well with the Battle Rifle.
 * It will give you a lengthy advantage over players with lower settings because you can turn faster than them. Sometimes you'll actually be able to run circles around them.
 * Face Painting is applied more.

Advantages of a low setting

 * Aiming is easier to control.
 * In Halo 2, any sensitivity above 5 will decrease the accuracy of the Battle Rifle and Sniper, as the auto-aim will stop working if a player moves their reticule too fast.

Trivia
Halo PC is unique among Halo games for offering separate settings for horizontal and vertical look sensitivities.