There are two use cases for the drop PDB operation.
Destructive Drop :
The first is the obvious one, when the PDB simply is not needed any more. This would be common in a non-production environment where a PDB that represents a starting point for a specific development task, or is under investigation, is repeatedly cloned and dropped.
Syn : - drop pluggable database PDB_1 including datafiles;
The unplug PDB operation leaves the PDB still known in the the root’s metadata; and its datafiles are still listed in the CDB’s control file. This is so that RMAN backup can be used to record the state of just this one PDB as it was at the moment it was unplugged. Therefore, whether or not a backup is to be made, the unplug PDB operation must always be followed by the drop PDB operation — either immediately, if no backup is to be taken, or after the backup is completed successfully. Of course, the intention of theplug in PDB operation implies that the datafiles must be retained.
Syn : drop pluggable database PDB_1 keep datafiles;