I hesitate to step in here and add to this because I really don't have time to invest in this conversation, but I don't think that everyone understands the concept that Magnus is proposing.
Using a template does not add complexity to a page.
It is simply a way of reusing information over and over again. If that information needs to change, you change it in one place, and all of the pages that are using that template are also automatically updated.
Magnus can correct me if I'm wrong, but I think he was using this "hatnote" template as an example of how that can be done.
It could be used to make the look and feel consistent for each category page that a project uses. Here's a simple example:
If you had a project called FRUIT, and you wanted to have a category page for each type of fruit, you could create a template that looked something like this:
{FruitCategory | color | shape | nutritional value}
For the Apple category page, your template would be entered like this:
{FruitCategory | red | round | Vitamin C = 100%}
The template could spit out something like this:
This page is about apples. They are red and round and provide 100% of Vitamin C.
It's important to eat fruits high in Vitamin C ... blah blah blah
If you were looking for other round fruits, click here.
If you would like to buy apples, contact soandso@gmail.com.
For the Orange category, you would have:
{FruitCategory | orange | round | Vitamin C = 100%}
The text could spit out this:
This page is about oranges. They are orange and round and provide 100% of Vitamin C.
It's important to eat fruits high in Vitamin C ... blah blah blah
If you were looking for other round fruits, click here.
If you would like to buy oranges, contact soandso@gmail.com.
The basic text in the above paragraphs is contained within the definition of the template, and the variables (in bold) are supplied when the template is used on a specific category page. The variables are added between the pipes ("|") and would be different for each Category page. The email address is the contact info for the Fruit project leader, and if that leader changes, you change that email address on the template, and it's automatically changed wherever this template is used.
You can think of it as a way of adding a "header" (a.k.a. "hatnote") to each page in a project, or it could be used to place an infobox on a category page like the Swedish one that Magnus showed below. The same template could be used for other countries by replacing the link to the Swedish flag w/ a link to that country's flag as well as links to that other country's project information.
It might seem complex on the surface, but it actually simplifies things.