Some mechanical systems whether they produce rotary motion or linear motion usually need to cease moving for one reason or another. Most pneumatic systems cycle and have a soft material stop to avoid banging and the vibration produced. In cases where free fall from the pull of gravity needs to have a “soft landing”  or “Braking”; rotary viscous dampers can help. I also look at it as an energy saving device and a safety device.  With a spring loaded damper we can absorb the free fall load to prevent loud noises and vibrations that can damage delicate devices. The internal spring resets the damper to accept the next load cycle.  Engineers see the need for this type of control for the reasons stated. A rotary viscous damper is one of those devices that once you see its benefits you keep it in your mental engineering tool box for future applications.  our website is www.mmtech.us