A compensator is a Barrel Attachment that redirects gases upward, reducing vertical recoil. The increased sound pressure will cause the player to show in the minimap from farther away, and increased weapon bulk reduces accuracy when firing from the hip.
The compensator helps reduce the amount the weapon will climb when fired due to recoil. The compensator increases your starting cone of fire size by 25% when firing from the hip. Cone of fire size while aiming down the sights is unaffected.