Connected pages provide a way to share content between different pages. When looking at a particular page in Edit mode in the Web Author application, one of the available commands is Create Connected Page. If this command is chosen, the author is led through a series of pages to select a destination channel, a template gallery, and then a template within that gallery. If any of the placeholders in the chosen template are named the same as the placeholders in the template used by the original page, they will automatically adopt the same content. (If none of the placeholders have the same name, it is not particularly useful to create the connected page in the first place.) Placeholders with unique names must be given their own content.
This means that template designers must be involved in the process of creating Web sites that use connected pages. The template designers need to create families of similar templates that contain placeholders designed to hold the same content, and importantly, that have the same names. Presumably, other things about the templates are different, such as other placeholders being present or absent, and formatting.