The Widget Cache feature is available in the premium version. You can reduce the number of sql queries with this feature.
When “Cache System” is enabled, the page is saved as a static html file, thus PHP and MySQL does not work for the page which has been cached. MySQL and PHP work to generate the html of the other pages which have not been cached yet.
Every time before the cache is created, the same widgets are generated again and again. This feature avoids generating the widgets again and again to reduce the sql queries.
Exclude a Widget
Although you have excluded the widget cache option, you may not be able to see the current data. If the content of a widget is printed directly on the screen via PHP, you cannot see the latest data since the whole page is saved as a static html file.
You should get the data via Ajax request instead of PHP directly to solve this problem.
Note: The widget panel has been changed after v5.8 of WordPress so you need to use the Classic Widgets Plugin to use this feature.
Update a Widget
If you update a widget, the widget cache folder which is /wp-content/cache/wpfc-widget-cache/ is deleted.
Clear Widget Cache
We did not add this feature not to confuse. You can clear the widget cache with two ways;
1. if you clear cache, the widget cache is cleared as well
2. if you update a widget, the widget cache is cleared
Number of DB Queries
If you wanna see the the number of database queries during the WordPress execution, you should add the following line into the footer.php of theme file.
<?php echo get_num_queries();?>