What is "Advanced Mode" in Views 3? In this article the first instruction is 


  On every site, run drush vd to turn the Views settings to the advanced mode.


What does this mean? A Google search for "Views advanced mode" yields mostly just links back to this article. What is "advanced mode"?
Advanced mode means 


  Set the Views settings to more developer-oriented values.


You can check the definition of this in views module Drush folder views.drush.inc file.

  $items['views-dev'] = array(
    'callback' =&gt; 'views_development_settings',
    'drupal dependencies' =&gt; array('views'),
    'description' =&gt; 'Set the Views settings to more developer-oriented values.',
    'bootstrap' =&gt; DRUSH_BOOTSTRAP_DRUPAL_FULL,
    'aliases' =&gt; array('vd'),
  );


Once drush vd command is executed following variables are set.

  variable_set('views_ui_show_listing_filters', TRUE);
  variable_set('views_ui_show_master_display', TRUE);
  variable_set('views_ui_show_advanced_column', TRUE);
  variable_set('views_ui_always_live_preview', FALSE);
  variable_set('views_ui_always_live_preview_button', TRUE);
  variable_set('views_ui_show_preview_information', TRUE);
  variable_set('views_ui_show_sql_query', TRUE);
  variable_set('views_ui_show_performance_statistics', TRUE);
  variable_set('views_show_additional_queries', TRUE);
  variable_set('views_devel_output', TRUE);
  variable_set('views_devel_region', 'message');
  variable_set('views_ui_display_embed', TRUE);
  $message = dt("Setup the new views settings.");
  drush_log($message, 'success');


You can do it with out using drush command too by navigating to "admin/structure/views/settings"