COMPRESS
Simply: COMPRESS=n - Allocated space in database for imported table will be exactly as the space required to hold the data.
COMPRESS=y - The INITIAL extent of the table would be as large as the sum of all the extents allocated to the table in the original database.
In other words:
The default, COMPRESS=y, causes Export to flag table data for consolidation into one initial extent upon import. If extent sizes are large (for example, because of the PCTINCREASE parameter), the allocated space will be larger than the space required to hold the data.
If you specify COMPRESS=n, Export uses the current storage parameters, including the values of initial extent size and next extent size.
If you are using locally managed tablespaces you should always export with COMPRESS=n
CONSISTENT
Default: n. Specifies whether or not Export uses the SET TRANSACTION READ ONLY statement to ensure that the data seen by Export is consistent to a single point in time and does not change during the execution of the exp command.
You should specify CONSISTENT=y when you anticipate that other applications will be updating the target data after an export has started.
If you use CONSISTENT=n, each table is usually exported in a single transaction. However, if a table contains nested tables, the outer table and each inner table are exported as separate transactions.
If a table is partitioned, each partition is exported as a separate transaction.
Therefore, if nested tables and partitioned tables are being updated by other applications, the data that is exported could be inconsistent. To minimize this possibility, export those tables at a time when updates are not being done.