Rule 7 of 8 · Chapter III — Solutions & ALM
Managed goes out; unmanaged never leaves dev.
Why this rule exists
Unmanaged imports merge into the target's default layer permanently — you cannot cleanly remove or service what you shipped. Managed keeps your work in its own layer with a real uninstall.
In practice
Export --managed for test and prod. The unmanaged solution exists only in dev and in source control.