Page types give concrete5 users a powerful way to create reusable page templates built using different designs and structures. Page Type Defaults extends this concept, allowing administrators to define "default" blocks to be automatically added to pages when they're created. If you know that pages of a certain type will always need to have a block of a certain type placed in a certain area of the page, Page Type Defaults is precisely the tool you'll want to use.
Even content itself can be pre-populated when a new page is created, saving editors and site contributors a lot of time that might otherwise be spent deploying duplicate content many times over. In practice, this can make setting up a complex page very easy, and allows an administrator to grant the privelages needed to create complext new pages to relatively nontechnical users.
From Pages & Themes > Page Types, we see a list of all page types currently installed on our site. Next to each, we see a button labeled Defaults. This will proivde us an editable "Default" version of a page type to be used as a master template of sorts for new pages created using that page type. Any blocks and settings we place on this page will also be placed on any new pages utilizing this same page type.
Already-existing pages that have this page type selected will not be affected, unless we use Set up on Child Pages (see below).
Set up on Child Pages
This option allows us to "push" content from the default page type defaults to evey page on the site that currently uses that page type.