Using design dialog we can store inputs globally for all templates using a design.
Basically design dialogs allows you to store configurations that can be accessed across pages. Data entered in design dialog input box is stored at \etc\design\design_name\jcr: content for each template. Update from a design dialog will be reflected across all pages created using the same template.
1. By naming a dialog as design_dialog , we specify that data will be stored globally and not at \content location.
2. By creating a design and attaching the design to the page , we specify the location of the where input will be stored.