As he writes in his posting this can be very useful for testing if you have to do some time traveling…
In our company we used a different approach by writing a setSYSDATE and getSYSDATE method which has to be used instead of SYSDATE. But the trick to just set
ALTER SYSTEM SET fixed_date = '2007-01-27-11:50:00';
is much easier and also works if a developer has used SYSDATE. For details and what other commands you have to issue, check out Dietmar’s posting.