One of the addition benefits of Template (beyond what merlyn said), is that Template is language neutral, and as WAP-enabled sites become more common, using Template over HTML::Template may become beneficial, since all you need to do for delieving WAP vs HTML is change the template file; you should not have to touch any perl code save to point the Template processor to the right place. And then adding text-only becomes simplier as well.
in reply to Web Application Frameworks and their Templating Engines with a Comparative Study of Template and HTML::Template
But regardless of the templater that you use, spliting perl code from HTML is one of the most benifical thing you can do with for your CGI.
Dr. Michael K. Neylon - email@example.com
"You've left the lens cap of your mind on again, Pinky" - The Brain