In Chapter 7 of Modern Engineering for Design of Liquid propellant Rocket Engines by Huzel and Huang, mentions the following engine cut off procedure.
The cutoff sequence usually consists of shutoff of subsystems ....
... and, in the case of test firings, postfiring securing (purges, flushes).
Why is it important to purge? And how is the system purged- only the fuel line or both the propellant feed lines?