If sqlldr needs to load a large amount of data, the time Oracle spends writing redo logs and archive logs at load time will take up a large portion of the total load time and can't be ignored; at the same time, it will also generate a large number of archive log files that will eat up your disk space.

In order to save time writing redo logs and disk space consumed by writing archive logs, you can specify that sqlldr does not generate redo messages for newly loaded data at load time, which will result in faster loading speeds and save a lot of space in the archive logs, but the newly loaded data will not be protected from future media recovery.

Because, in the previous backup, there was no just-loaded data, which is easy to understand; and, you use unrecoverable, then there is no detailed description of the newly-loaded data and the loading action in the log. If the data file is corrupted at this point, the just-loaded data is obviously unrecoverable.

The conclusion is that unrecoverable improves the speed of loading, and it is recommended that you take a backup of the database, or at least of the tablespace, immediately after the load is complete.