There are templates you can choose when building pages that make advanced formating easier, like splitting the section below in half (stacked on smaller screens).
When you use Layout 12 as a page template you still get the option to add sub content in the editor. This content won't show up on the main page (or on the admin page), but will be there if you change layouts. This is useful if you have content you only need to show periodically. By switching the layout to say, layout 11, would reveal the sub content section, acting as a kind of switch.
The same goes for the image and video galleries, the links list and the audio player. By changing the placement to sub in the module settings, you can hide instead of delete them. Of course, any module in the sub section will show up if you change layouts.