Protect the database from data loss due to failures

… that some or all of your data files are lost or damaged. Typically, this situation is caused by a media failure or accidental deletion. Your goal is to return the database to normal operation by restoring the damaged files from RMAN backups and recovering all database changes.

Purpose of Flashback and Database Point-in-Time Recovery says:

Typically, the following situations call for flashback features or point-in-time recovery:

A user error or corruption removes needed data or introduces corrupted data. For example, a user or DBA might erroneously delete or update the contents of one or more tables, drop database objects that are still needed during an update to an application, or run a large batch update that fails midway.

A database upgrade fails or an upgrade script goes awry.

A complete database recovery after a media failure cannot succeed because you do not have all of the needed redo logs or incremental backups.

In these situations, you can use point-in-time recovery or flashback features to return the database or database object to its state at a previous point in time.

Purpose of Block Media Recovery says:

You can use block media recovery to recover one or more corrupt data blocks within a data file. Block media recovery provides the following advantages over data file media recovery :

Lowers the mean time to recover (MTTR) because only blocks needing recovery are restored and recovered

Enables affected data files to remain online during recovery

Without block media recovery, if even a single block is corrupt, then you must take the data file offline and restore a backup of the data file. You must apply all redo generated for the data file after the backup was created. The entire file is unavailable until media recovery completes. With block media recovery, only the blocks actually being recovered are unavailable during the recovery.

Block media recovery is most useful for physical corruption problems that involve a small, well-known number of blocks. Block-level data loss usually results from intermittent, random I/O errors that do not cause widespread data loss, and memory corruptions that are written to disk. Block media recovery is not intended for cases where the extent of data loss or corruption is unknown and the entire data file requires recovery. In such cases, data file media recovery is the best solution.