Managed vs. Unmanaged BO
What it is
Two RAP implementation types. A managed BO lets RAP handle persistence (create/update/delete to the DB) for you — ideal for greenfield. An unmanaged BO delegates persistence to your existing code (legacy tables, function modules) — for wrapping a brownfield application.
Why it matters for Clean Core
Choosing managed where you can keeps the implementation tiny and Clean-Core-native. Unmanaged is the bridge that lets you put a RAP/OData face on legacy logic without rewriting it all at once.
Common pitfall
Defaulting to unmanaged because it 'feels closer to classic ABAP'. Unmanaged means you re-implement create/update/delete/lock yourself. Prefer managed (with optional 'managed with additional save') unless you must reuse legacy persistence.