Explanation

Always Encrypted supports two types of encryption: randomized encryption and deterministic encryption.
* Randomized encryption uses a method that encrypts data in a less predictable manner. Randomized encryption is more secure, but prevents searching, grouping, indexing, and joining on encrypted columns.
* Deterministic encryption always generates the same encrypted value for any given plain text value.
Using deterministic encryption allows point lookups, equality joins, grouping and indexing on encrypted columns. However, but may also allow unauthorized users to guess information about encrypted values by examining patterns in the encrypted column, especially if there is a small set of possible encrypted values, such as True/False, or North/South/East/West region.
References:
https://docs.microsoft.com/en-us/sql/relational-databases/security/encryption/always-encrypted-database-engine