What Is Partitioning?
Partitioning is a way of spreading tables and indexes physically, by keys, across two or more tablespaces. The Oracle cost-based optimizer is smart enough to recognize partitions and identify the best way to return rows. Partitioning also aids in backups and recovery by being capable of performing these functions on significantly less data, which means it takes far less time to back up a tablespace as well as recover it (should the need arise).
TIP
It has been my experience that the more one can divide up the disk I/O across disk drives, the better Oracle will perform. The best reason for partitioning Oracle tables and indexes is to break an otherwise large object into smaller, more manageable pieces, both from a data-access point of view and from an availability point of view.