Use Landing Pages for high-level, main pages and large sections of content that needs careful, editorially controlled structure.
Functionally, a Landing Page allows additional functionalities that may not be available with other content types (such as Topic Pages) in GovHub.
For example, with a Landing Page you can:
Drag and drop content as opposed to working solely within the parameters of a text editor box.
Access full-width of a page (optionally, as opposed to defined space reserved for the side navigation)
Select from more defined sections (as opposed to a more fluid layout)
Important Note: Don't use a Landing Page for low-level, detail pages or content that should use a specific, pre-structured content type (such as Event, News, How Do I, etc.).