Using a multi-tenant SQLite setup helps ensure user data is separated into their own databases and won't be inadvertently queried by other users. Users can then choose to share the data they want to either via peer-to-peer or by aggregating to a postgres database.
But the main benefit to me would be that user data will be more private and protected and configurable.
This gives someone much more fine-grained control over their data and how their data is stored. I think it ultimately makes the attack vector space smaller for any client data.