What is the difference between “create_users” and “add_users” capabilities?

The codex lists both create_users and add_users under roles and capabilities.

Does anyone know what is the difference between these two?

I explored WordPress to find difference between it and in schema.php file i found the following function only where in WordPress add_users capability is used.

/**
 * Create and modify WordPress roles for WordPress 3.0.
 *
 * @since 3.0.0
 */
function populate_roles_300() {
$role =& get_role( 'administrator' );

if ( !empty( $role ) ) {
    $role->add_cap( 'update_core' );
    $role->add_cap( 'list_users' );
    $role->add_cap( 'remove_users' );

    // Never used, will be removed. create_users or
    // promote_users is the capability you're looking for.
    $role->add_cap( 'add_users' );

    $role->add_cap( 'promote_users' );
    $role->add_cap( 'edit_theme_options' );
    $role->add_cap( 'delete_themes' );
    $role->add_cap( 'export' );
}
}

Based on the comment written in code i think that the add_users capability is only used for backward compatibility and can be removed in future version of WordPress so we should use create_users capability instead of add_users capability.