Hi Lars,
Hook Elements in simple terms are actions hooks. They run at specific points as your page loads, depending on which hook you use. In general, you only use this if you’re running code you wish to run at a specific location.
Otherwise, some code need to run on page load or sometime early as your page loads. If you add a code like add_shortcode
in an action hook/hook element, it will be loaded late which may cause issues.
Simply put it, some code won’t work in Hook Elements.