What is the Divi Library and why save or load an existing layout:
The Divi Library is place that stores pre-made layout templates as well as your custom saved layouts, modules and widgets (Divi > Divi Library).
Save a layout to the Divi Library if you would like to use it as a template for other posts or pages. This will cut down on the creation time needed for those future posts or pages.
To Load a Original/Saved Sections from your Divi Library:
This is a good option if you want reset your page and rebuild a demo page again (You have all demo page layouts in Divi Library).

- Create a new page or edit an existing page and enable the Visual Builder.
- Click on the Add New Section icon

- Click on Add From Library Tab.
To Save a Section in your Divi Library:
- Edit any page that contains a Divi Section and enable the Visual Builder
- Hover over the section you want to save to Divi Library.
- Click on the Save Section to Library icon

- Give the Section a descriptive name.
- Click on the Save To Divi Library button.