Imagine that you had a static website that had a few dozen pages of information. In order to make navigation easier, you may want to include a navbar on all of your pages. You likely would like to only have to edit the navbar in one location, and have all your webpages be updated accordingly. You have a few serious options: 1. Using PHP, add an include directive to your html files and either dynamically or statically include a navbar 2. Add a script to your page which modifies the DOM client-side and inserts a navbar 3. Use a web framework that allows you to insert arbitrary html/css/js server-side.
This library allows you to do the first option, statically, without the reliance on PHP.
You could. PHP can generate static files. Here's a script on Stack Overflow that does exactly that. You would even get more features with PHP. But if you can't use PHP for whatever reason, want to process html server-side, and don't want to lock yourself into a JavaScript framework, then this crate checks all those boxes.