When the database is running out of space and you may need to take action to free up some space as soon as possible. Which tables to shrink? However, which tables should be shrunk? In Oracle 10g, DBMS_ADVISOR do the job to help help you(DBA ;-) to identify which tables should be shrunk by comparing the actual used space with HWM.

--create a table to store the output of DBMS_ADVISOR

create table result
(   
owner varchar2(30),
table_name varchar2(30) not null,
checkdate date,
task_id number not null,
task_name varchar2(30),
message varchar2(4000),
more_info varchar2(4000)
);


--loop through all the tables owned by user USER1
DECLARE
Task_Name   VARCHAR2(100);
Task_descr  VARCHAR2(100);
Object_Id   NUMBER;
Task_Ida    NUMBER;
BEGIN
Task_Name := ''; -- a unique  task name genetered by create task

FOR Cur IN (SELECT   *
FROM     User_Tables
WHERE    TableSpace_Name IS NOT NULL
ORDER BY Table_Name)
LOOP
Task_descr := 'Table usage in '
||Cur.Table_Name;

Task_Name := NULL;

dbms_Advisor.Create_Task('Segment Advisor',Task_Ida,Task_Name,Task_descr,
NULL);

dbms_Advisor.Create_Object(Task_Name,'TABLE','USER1',Cur.Table_Name,
NULL,NULL,Object_Id);

dbms_Advisor.Set_Task_Parameter(Task_Name,'RECOMMEND_ALL','TRUE');

dbms_Advisor.Execute_Task(Task_Name);

INSERT INTO Result
SELECT Owner,
Cur.Table_Name,
SYSDATE,
Task_Id,
Task_Name,
Message,
More_Info
FROM   dba_Advisor_Findings
WHERE  Task_Id = Task_Ida;
END LOOP;
END;

References:
http://www.oracle.com/technology/oramag/oracle/05-may/o35tuning.html
Metalink Doc ID:242736.