It is easy to accidentally pollute the global PHP scope with unneccessary vars, and in some cases these vars are classes or objects, and can be a huge waste of memory per php process.
This php will loop through all global vars, then sort them by the strlen of their json_encoded value.
6788535 => 'GLOBALS', 5615030 => 'wp_object_cache', 2516754 => 'wpdb', 303154 => 'wp_filter', 51323 => 'wp_scripts', 36602 => 'wp_post_types', 14685 => 'wp_taxonomies', 14590 => 'submenu', 14576 => 'wp_registered_widgets', 13426 => 'wpseo_sitemaps', 13111 => 'wp_registered_widget_controls', 10468 => 'wp_rewrite', 10203 => 'AA_DEBUG', 9237 => 'wp_styles', 8861 => 'allowedposttags', 8568 => 'wp_roles', 7017 => 'wp_registered_widget_updates', 5727 => 'menu', 5383 => 'wp_widget_factory', 4355 => 'allowedentitynames', 4300 => 'wp_post_statuses', 3091 => 'userdata', 3003 => '_SERVER', 2769 => '_parent_pages', 2658 => '_wp_admin_css_colors', 2393 => '_registered_pages', 2283 => 'wp_registered_sidebars', 2106 => 'wp', 1861 => '_wp_post_type_features', 1477 => 'mb_news_links', 1468 => 'mb_the_brief', 1463 => 'mb_top_stories', 1461 => 'mb_project', 1383 => 'current_screen', 1363 => 'wp_file_descriptions', 1336 => 'wp_locale', 1322 => 'admin_page_hooks', 1137 => 'sidebars_widgets', 1131 => 'wp_query', 1071 => 'shortcode_tags', 1004 => 'BetterRelatedAdmin', 956 => 'merged_filters', 840 => 'wp_actions', 809 => 'relevanssi_variables', 775 => 'l10n', 764 => 'mwm_aalLoader', 754 => '_wp_deprecated_widgets_callbacks', 654 => 'new_whitelist_options', 591 => 'members', 543 => 'wp_embed', 509 => 'wp_admin_bar', 422 => 'dsq_api', 409 => '_wp_additional_image_sizes', 376 => 'acf', 344 => '_REQUEST', 341 => '_scb_data', 339 => 'allowedtags', 285 => 'month_abbrev', 284 => '_wp_real_parent_file', 261 => 'month', 226 => 'wp_meta_boxes', 224 => '_wp_registered_nav_menus', 175 => 'weekday_abbrev', 161 => 'weekday_initial', 133 => 'weekday', 119 => '_wp_theme_features', 112 => '_wp_submenu_nopriv', 96 => 'ISCLOG', 87 => 'count', 86 => 'wp_theme_directories', 78 => 'core_menu_positions', 42 => 'custom_post_type_order', 37 => 'akismet_api_host', 36 => 'timestart', 32 => 'wpseo_sitemaps_admin', 31 => 'user_email', 30 => 'args', 28 => 'PHP_SELF', 26 => 'akismet_nonce', 24 => 'members_load', 23 => 'wpseo_admin', 22 => 'hook_name', 20 => 'tinymce_version', 18 => 'hook_suffix', 16 => 'parent_file', 13 => 'title', 12 => 'time_format', 11 => 'is_configured', 10 => 'required_mysql_version', 8 => 'wp_db_version', 7 => 'taxnow', 6 => '_wp_menu_nopriv', 5 => '_wp_last_utility_menu', 4 => 'separator_found', 2 => 'show_admin_bar',