The Order Preserving Encryption scheme is an ideal candidate to choose when the order of the encrypted content (alphabetic/numeric sort order) must be preserved, and also when searches will be run on this ordered data. This encryption scheme also preserves a prefix search.
Use Case: FirstName/LastName of an Account /Contact/Person Account objects, when you want these fields to be searchable and maintain their sorting order.
IMPORTANT: This scheme is the highest functionality and lowest security encryption scheme. Take care when assessing the tradeoffs associated with its use.