is there a benefit in using a constant over get_stylesheet_directory_uri?

You can read up the source code of theme.php where get_stylesheet_directory_uri() is defined, inside you’ll see a str_replace() wich is consuming additional resources on each request. The best way to avoid this is to define a variable or constant that contains the path. In that case it is only called once.

https://core.trac.wordpress.org/browser/tags/4.3.1/src/wp-includes/theme.php#L0