The append mode is the default during a parallel insert operation: data is always inserted into a new block, which is allocated to the table. Therefore, the APPEND hint is optional. You should use append mode to increase the speed of INSERT operations, but not when space utilization must be optimized. You can use NOAPPEND to override append mode.
The APPEND hint applies to both serial and parallel insert operation: even serial insertions are faster if you use this hint. The APPEND hint, however, does require more space and locking overhead.
You can use NOLOGGING with APPEND to make the process even faster. NOLOGGING means that no redo log is generated for the operation. NOLOGGING is never the default; use it when you want to optimize performance. It should not typically be used when recovery is needed for the table or partition. If recovery is needed, be sure to perform a backup immediately after the operation. Use the ALTER TABLE [NO]LOGGING statement to set the appropriate value.