Ameya,
Great observations and questions. You are correct about the attributes of entities stored at each level.
Managed - Data, profile, and sample all in Catalog
Registered - Profile and sample in Catalog
Addressed - Technical metadata (schema) in Catalog
The benefit of having data at each of these levels is that an organization can Catalog and document ALL of their data assets without incurring the burden of keeping a resident copy of it all in the Catalog. For infrequently utilized sources, addressed can be an option. A good example might be tables that are needed once a year for audit purposes. These can be promoted to managed when needed and then demoted when you are done. They are still in the Catalog but the data isn't resident.
Registered is an enhancement between addressed and fully managed, allowing you to keep a profile and sample data to further enhance end users' understanding of the entity. When utilized for a publish or prepare activity these registered entities are temporarily promoted to managed in order to operate on them. As such, the consideration between keeping something registered or managed comes down to how often they are utilized. If there are lots of requests to use a registered entity you may want to consider making it a managed entity so that you can load it once and use it often.
Of course, depending on the usage patterns and the mix of registered and managed entities, system configuration and storage need to be taken into account.
I hope this helps.
