Difference between Custom Post Types and Templates?

Hello,
i created a custom post type and a template with the name single-customposttypename.php. But what is the difference if i solve an issue with the creation of a new custom post type and the respective template or to create a new template for pages in general?

Is the only difference that custom post types are more “seperated” from the other pages and the wordpress admin panel offers an entry in the menu for custom post types?

Can somebody explain the diference to me?

Thanks.