### Reference : - **Definition:** - References the contents of a external USD files and/or layers created by other LOP nodes into a branch of the existing scene graph tree. (Super object merge) - **Use Cases:** - Bringing in large assets or environments maintained separately. - Sharing common assets across multiple shots or scenes. - Keeping scene composition modular and manageable. - Allow to change hierarchy in scene graph when imported - ### Sublayer: - **Definition:** Adds an external USD file as a sublayer to the current USD layer stack. This node represents the most basic way to add USD files to your scene. Sublayers tell USD to add the content primitives your scene as-is, without any sort of parenting of the primitives - **Function:** The sublayer's contents are merged into the current layer stack, effectively layering the data. - **Use Cases:** - Sublayering animation - Building up a USD stage by layering multiple files. - Overriding or extending data from a base USD file. - Creating variations or versions by layering changes. - don't allow do change hierarchy in scene graph when imported ### Merge :  - **Function:** Merge combines multiple layer stacks into a single flat list of sublayers. It takes the sublayer hierarchies from all inputs and flattens them into one linear list under the root layer. - **Use Cases:** - **Simple Combinations:** When you need to combine layers without complex hierarchy requirements - **Performance Optimization:** When you want to avoid nested sublayer complexity