To keep existing menus and their content when changing the whole site design.
For example, I want to change my site design from a Ludwig based one, to a Nix based one. But I have to create and set up all my menus and their corresponding pages all over again. The menus and their pages should be able to be saved or not altered when switching site designs.
Alan Magner commented
Allow customizations (menu, background images, content blocks, etc) to migrate to a new site design. Currently if we want to refresh the look of our websites we will have to customise every single folder and tab from scratch after choosing a new site design. Allow pre customizations (menu, background images, content blocks, etc) to automatically migrate to the new site design.