Most people do not and should not need this file.
Do you have a third-party keyboard attached? This file keeps track of the layout for the keyboard that’s connected, if it’s not known. Your internal one should be recognized already, and won’t need the file.
If you do have a third-party external keyboard, and it’s set up incorrectly, delete the plist file if it’s there, and when you restart and login, the Keyboard Assistant should pop up right away. (It’s also hanging out in /System/Library/CoreServices. I think the app does nothing unless you have an unrecognized keyboard attached.)