Question

why avehical are fitting with shocker

Answer 1

For your comfort and safety. If you go over a bump without dampers in place the springs will simply oscillate. You will get an uncomfortable bouncy ride and the car will have less available mechanical grip for turning and stopping.

A damper (what you call a "shocker") resists the bounce by forcing oil through narrow openings. The energy of the spring heats the oil inside the damper instead of bouncing the car up and down