The second use case is about reusing content from one page from a number of other pages.

The Excerpt Macro allows to define content on a page for reuse. The content can then by displayed in another page. The projectdoc Toolbox calls this feature transclusion. The content is defined with the Section Macro (if it has a title and a body) or the Content Marker Macro (for any other part of a page that needs to be transcluded).

While the excerpt macro may only provide one content on a page for reuse, the projectdoc macros may be used any number of times and provides some enhanced transclusion features.

To render the content on another page, Confluence provides the Excerpt Include Macro. The projectdoc provides the Transclusion Macro to do this. But transclusion (especially with sections) is provided by a number of other macros.