The LoadedOnlyWhenReferenced property is a property that can be used to only load content when it is used in a game. This is can be used for optionally loaded content – that is, content which will only be loaded based off of certain conditions in the game (such as the current level being played).
When to use LoadedOnlyWhenReferenced
LoadedOnlyWhenReferenced is very useful if you have content in your game which is optionally loaded depending on the state of your game. For example, you may have a game where levels are represented by .scnx files. You may add multiple .scnx files to your Screen and mark them as LoadedOnlyWhenReferenced. This means that by default no files will be loaded when your Screen is created. However, if you access any properties created for the files in the Screen, then the corresponding file will be loaded.