what is its job?

 

exactly what it sounds, it dampens pressure. if it fails, it can cause too much pressure and can overwork injectors, cause flooding, no starts etc. etc.

 

Imagine a garden hose without a nozzle. The nozzle regulates the amount of water flowing through as well as the pressure it comes out at.

 

cut & paste from Whiplle Industries - whats a fuel damper do?

A damper is critical to the proper function of any EFI setup. Rapid cycling of the fuel injectors and fuel system components in a running engine combine with the non-compressibility of the fuel; and create high frequency pressure waves in the rail. These pressure waves can cause substantial variation in the fuel delivered by the injectors; causing numerous running problems that are difficult to trace, in addition to increasing stress on the fuel pressure regulator

rgds
mikr