A 12c Multitenant Database is designed to make consolidation easier. The PDBs have not only their application data in separate tablespaces, they also have their application metadata in separate SYSTEM tablespaces. That’s what makes it so easy and fast to unplug a PDB.
The SYSTEM tablespace of the CDB contains the internal metadata that is shared by all PDBs. Internal metadata (the dictionary tables) and internal objects (like the DBMS* packages) (more...)