The default WP stuffs, like Pages, Posts, Blog (latest posts - index.php) must work without plugin.
So, you can have some more features for example on Posts (single.php) page after you install the plugin, but the default one, like Featured image, tags, category, post date, post title, navigation between posts… must work without plugin.
For example, usually on Post (single.php) I have custom field to add the content above the post title (slider or video or some iframe or image) but this layout can not be done without plugin and that is ok.
On other side, I usually set featured image to be placed bellow the page title, and this must work no matter if the plugin is active or not - because the feature image is the "default’ function in WP.
So, again, the point is to have all default WP functions there without plugin.