If you want to save the value of a variable so that it's reinitialized when the app restarts in the future, use this action. Note that the value of the variable at the moment this action is executed is what will be saved. It does not flag a variable to perpetually persist its value each time it is upated. It's up to you to implement that behavior if that is what you want.
The variable will be saved so that the next time the app launches its value will be restored.