A lot of WordPress themes include custom page templates. These can be used to create a different layout than the standard page.php file. Originally this was used (and is still a valid use-case) to provide just a marginally different layout such as removing the page’s sidebar.
As the WordPress ecosystem grew so did the use cases for custom page layouts. Separately styled pages for eCommerce cart & checkout pages, account pages, contact pages, and more became very common. The developer documentation for page templates suggests that these one-time use templates should not be given the traditional PHP comment header to avoid having them appear in the “Page Attributes” meta box.
(more…)