Any absolute MUST reason for a DMZ?

From: Rock (
Date: 05/19/05

Date: Wed, 18 May 2005 23:51:47 GMT

Is there any absolute *must have it* reason for a DMZ?

Would the judicious use of port-forwarding be an alternative? As long
as I know each app's port, I think I could use the router to block
unwanted ports.

Maybe the only reason is the router won't tell me if there's a DOS
attack going on. And looking at the logs, I think the log filtering
is "natto-so-good-o". (you need some Japanese to get that one).

But I can't think of another reason. Any others?