I think the advantages of this in a digital age are vastly overblown. If an extremist government comes to power they won't care and they can just do the SQL join. Let it go to court, the extremist government will decide anyway so the outcome is already predetermined.

Compare this to a physical storage of paper documents that need to be SQL joined, the effort required is several magnitudes more.

What it is good for is data breaches, it effectively limits the data that can be leaked at once.