Should I use loop in the single.php file?

I read many tutorials, and checked many premium/free theme’s source and most of them use loop in the single.php file.

The single.php file only displays one post, so I think the_post() is enough, while is unnecessary. Is there any reason why these themes (twentyfifteen, twentytwelve, etc..) use loop in the single.php file?

Stricktly speaking, you don’t need the loop in single post pages, you only need the call to the_post().

The reason for the_post() is that the_post() sets the $post global value to the single post post object