The clever use of off-chain storage. If everything is stored on the chain, not only is it slow, but it also risks leaks; putting everything in a centralized database goes against the original intention of decentralization and is also vulnerable to hackers. Dusk's approach is very flexible: sensitive data is stored in encrypted offline repositories, and only a "fingerprint" (hash) pointing to this data is stored on-chain. If regulatory audits are needed, compliant personnel can verify by authorized access to these encrypted data, while outsiders without the key will at most see a string of gibberish, which is useless. This way, audit requirements are met, and user privacy is not exposed to the world during normal operations.