Queryable encryption was the main attraction at MongoDB World 2022, for understandable reasons. It introduces a unique capability to reduce the attack surface for confidential data in several use cases. In particular, data remains encrypted at insert, storage, and query. Both queries and their responses are encrypted over the wire and randomized for resistance to frequency analysis.
The outcome of this is that applications can support use cases that require searching against classified data while never exposing it as plaintext in the data store infrastructure. Datastores that hold private information are a main target of hackers for obvious reasons. MongoDB’s encrypted fields means that this information is cryptographically secure at all times in the database, but still usable for searching. In fact, the database does not hold the keys for decrypting the data at all. That means that even a complete breach of DB servers will not result in loss of private information.