What’s the difference between admin_url() and get_admin_url() functions?

Except for the $blog_id parameter (which is only allowed in the get_admin_url function), what is the difference between admin_url and get_admin_url?

The admin_url() function retrieves the URL to the admin area for your current site. You needn’t give the blog id for your current site. You can use this function if you aren’t running WordPress multisite. And use the get_admin_url() function to get a specific site URL in the multisite admin.