In helicopters with hydraulically powered flight controls, control forces from the rotor are not fed back to the Pilot. Without resistance, the flight controls would feel “dead”. This would be unsafe, because the Pilot loses force cues and control sensitivity awareness. 

“It can be installed on both the collective and the cyclic.” → CORRECT. An artificial feel system (also known as “Gradient feel” or “Stick feel” system) is a mechanism used in aircraft with hydraulically powered flight controls and it can be installed on both the collective to provide a consistent level of resistance or “friction” that prevents inadvertent movement, and the cyclic to assist with self-centering and tactile feedback. This system typically uses centering springs to create a force that increases as the control is moved further from its neutral position.

“It is used on the cyclic and yaw controls to reduce vibration.” → INCORRECT. An artificial feel system is not for vibration reduction. That is the role of the dampers.

“It is used only on the cyclic for self-centering of the control.” → INCORRECT. An artificial feel system is not limited to cyclic only. It can be applied to multiple control axes.

“It is used only to damp oscillations in the yaw axis.” → INCORRECT. An artificial feel system is not for yaw damping. The yaw damper / SAS is responsible for this.