Vary menu based on some logic (user role, current page, etc.)

functions.php

<?php
  // ...
  register_nav_menu( 'primary', __( 'Primary default location', 'yourtheme' ) );
  register_nav_menu( 'primary-subscriber', __( 'Primary subscriber location', 'yourtheme' ) );
  register_nav_menu( 'primary-account', __( 'Primary account location', 'yourtheme' ) );
  // ...
?>

header.php

<?php
  // ...
  $args = array(
    'theme_location' => 'primary',
  );
  if ( current_user_can( 'read' ) && !current_user_can( 'edit_user' ) ) {
    $args['theme_location'] = 'primary-subscriber';
    $args['walker'] = new Your_Walker_Class;
  }
  if ( is_page('account') ) {
    $args['theme_location'] = 'primary-account';
  }
  wp_nav_menu( $args );
  // ...
?>