SQL> ALTER TABLE TABLE_NAME enable ROW movement;

SQL> ALTER TABLE TABLE_NAME shrink SPACE;

SQL> ALTER TABLE TABLE_NAME disable ROW movement;

Benefits regarding to Oracle Documentation :

• Full table scans will take less time (a table scan will always scan up to the HWM even if space is not used)
• Better index access takes place because of a smaller B-Tree
• Space is freed up for other database objects
• Space below the HWM is released and the HWM is moved down

 Thank you
Osama Mustafa