Do you have files with millions or even billions of records? When such a file has to be changed, for example because a new field is added, copying the data can take hours.
Rapid Fire copies the data while the applications keep running. Instead of shutting down the system for hours or days, you are offline for a couple of minutes.
Frank Hildebrandt created Rapid Fire and wrote most of its RPG code on the IBM i. I have substantially extended the plug-in over the years.