Purpose of TZ_OFFSET()

What is the purpose of TZ_OFFSET()? For example,

select TZ_OFFSET('-3:0') from dual;
select TZ_OFFSET(sessiontimezone) from dual;
select TZ_OFFSET(dbtimezone) from dual;

just return their arguments. So what is the purpose of this function? If the only meaning is the to turn timezone name into offset value, then only the form TZ_OFFSET('time_zone_name') should be allowed but not the above 3 variants.

Also, the documentation said the return value dependent of the date the statement is executed, but why? Is it caused by daylight saving? Received on Sat Jan 29 2005 - 04:48:33 CST