What are the differences between Payloads and Reference, and when to use them.
Please have a look at the USD Terms and Concepts
Read the References section first, then the Payload section and follow the performance note at the end.
References are used to include other USD assets into a stage. This allows instancing of the asset.
Payloads are a special kind of References where you can decide dynamically if the data itself should actually be loaded into the stage or not. This is useful for huge stages where only parts of the assets are required for a specific operation.
So for the normal size projects it is better to use the references?