A BL becomes a Calculation Engine if it performs complex calculations, (e.g. an invoice calculation engine or an insurance simulator). Engines are usually subject to versions.
B
Logic to Synchronize data in CS's with an external system. Isolating this logic makes the CS completely system agnostic and it's easier to decouple or replace the external system.
C
Isolated Business Logic (Actions), to manage complexity, composition or to have its own 'ifecycle.
D
Reusable Core Services with public entities, actions, and blocks.
E
Technical wrapper to expose an API to External consumers, keeping core services system agnostic and supporting multiple versions of the API.