I would guess that most people who use HTML::Template do it because they have other people who are not perl programmers but need to work directly on the HTML layout -- no one (least of all the non-programmers) would want non-programmers altering contents of perl scripts just to change the appearance, layout or "static" information of a web page. Or maybe programmers have one text editor mode for perl and a different one for HTML, and it's just easier to do these two jobs in separate text files.

If those situations don't apply to you (you alone are controlling the static layout as well as the dynamic content and you handle HTML editing the way you handle perl editing), then this seemingly contradictory use of HTML::Template is simply a way of organizing your own code to be neater, more compact and easier to maintain -- and easier to adapt later on, if at some point you decide to use HTML::Template in the more usual manner, to keep the code and the layout completely separate.