ZSON learns on your common JSONB documents and creates a dictionary with strings that are frequently used in all documents. After that you can use ZSON type to compress documents using this dictionary. When documents schema evolve and compression becomes inefficient you can re-learn on new documents. New documents will be compressed with a new dictionary, old documents will be decompressed using old dictionary.
In some cases ZSON can save half of your disk space and give you about 10% more TPS. Everything depends on your data and workload though. Memory is saved as well. For more details see README.md.
Please don't hesitate to ask any questions. Any feedback and pull requests are welcome too! -- Best regards, Aleksander Alekseev