The Single Layout Builder provides users with a similar building interface to that of the Page Builder, allowing designers to take advantage of a drag and drop interface for crafting custom assets.
One primary difference here is that you are designing a repeating page template that will take advantage of database-driven Elements.
On top of that, you can assign your Single Layouts that you have created to different pages or posts on your website, as you can with the Archive Layouts and the Archive Layout Builder, allowing you to create complex site layouts that respond to the contextual needs of a particular area of your site.