Do you have a complex structure that you want to reuse in different layouts a complex modal or card layout and find it frustrating that you the need to recreate them each time for different layouts. Well now you can create an empty structure and by inserting it in your layout it pre-creates the rows/columns you need with all your carefully constructed class structures !
Simply create a new "Reusable Page Structure" and add the article structural elements you want with all the class names set. Now when you create/edit another layout you can simply insert this premade structure and all it will be generated for you automatically so that you can add the fields you want into it!
This differs from the mini-layouts in that the structure it recreated in your layout where the mini-layout is rendered in the frontend but cannot be changed in the layout editor