Parallel DDL is often used to create summary tables or do massive data loads that are standalone transactions, which do not always need to be recoverable. By switching off Oracle Database logging, no undo or redo log is generated, so the parallel DML operation is likely to perform better, but becomes an all or nothing operation. In other words, if the operation fails, for whatever reason, you must redo the operation, it is not possible to restart it.
If you disable logging during parallel table creation (or any other parallel DDL operation), you should back up the tablespace containing the table after the table is created to avoid loss of the table due to media failure.
Use the NOLOGGING clause of the CREATE TABLE, CREATE INDEX, ALTER TABLE, and ALTER INDEX statements to disable undo and redo log generation.