I googled the two word together but could not find anything. I have never used it. Is there any necessity for it although we have main.storyboard.
When you run your program in Xcode simulator gets open and your application gets open then you can see black white screen for fews seconds before actuals developed screen
Blank screen - LaunchScreen.storyboard - Non editable
Developed Screen - Main.storyboard - Editable for which you can able to make changes