Hierarchy Organizers, quite simply, allow you to organize your Scene Hierarchy in whatever way you wish, allowing you to group together related Asset Chunks or do whatever else you want.
They are entirely optional, however if you wish to use one, you will assign it to your World via its Optional Components window.
The primary reason for using a Hierarchy Organizer is for sanity's sake. When you begin working with Streamable Assets and your World starts growing and growing in scale, you will find that the number of root Game Objects in the scene grows to an almost unimaginable level. Not only does this make it harder to identify SAM related Game Objects, non SAM related Game Objects also become impossible to locate. Hierarchy Organizers allow you to make sense of the mess. In addition to this, there are also performance benefits to using a Hierarchy Organizer:
1) Having too many root Game Objects (game objects without parents) can have a negative impact on certain systems and Unity methods, especially ones that require searching the root objects in the scene.
2) Having a well organized hierarchy can allow you to perform faster searching, as you can usually reduce the size of the pool of objects that need to be searched.
3) It simplifies some operations, such as World Shifting, since you can perform the operation on a smaller subset of parent Transforms rather than on each individual Asset Chunk.
There is only one default Hierarchy Organizer included with the Streamable Assets Manager, the Standard Hierarchy Organizer.
Fortunately, this organizer is incredibly robust and gives you a tremendous number of options for how your hierarchy is setup. In addition, there is a built in World Shifter (the Standard Hierarchy World Shifter) that has been designed specifically to work in conjunction with it, reducing the amount of work you need to do even more!!
With that said, you always have the option to create a Custom Hierarchy Organizer as well. This chapter provides details for whichever option you choose. Enjoy!
Each Organizer is intended to represent a single Hierarchy. As such, unlike with most of the other components in the Streamable Assets Manager, each Hierarchy Organizer should only be used with a single World component.