The Total Theme Core plugin is a plugin included with the Total theme since version 4.9. This plugin extends the theme’s functionality via functions that are typically “plugin territory”. These include things such as custom meta options, custom widgets, custom post types (portfolio, testimonials, staff), custom shortcodes and custom WPBakery builder modules.
The reason these functions are within a plugin is if you ever decide you want to switch themes you can easily switch themes and keep these custom functions without having to re-add them to your new theme. There are also some benefits in terms of development by keeping things neatly organized within the theme and plugin as well as some benefits when it comes to troubleshooting issues on the site.
In terms of speed there is no difference between having these extra functions within the theme or inside a plugin, it causes zero affect on site speed and in fact when moving the functions out of the core theme into the plugin we managed to make things even faster and greatly optimize various functions!
While this plugin is not “required” if you do not activate the plugin you do miss out on all the extra goodies that come with the Total theme so it is highly recommended you enable the plugin for a full experience. Additionally there are functions in the Total Theme Core plugin that are only available for Total theme users so if you do decide to ever switch themes you may lose some none-core functionality from the plugin such as custom Google fonts and styling for your custom WPBakery blocks so we do recommend using the plugin only with the theme active for best results.
When it comes to updates this plugin will often be updated when the theme itself is updated. If you update your theme and there is a new version of the Total Theme Core plugin you will see a notification in your WordPress dashboard so you can proceed with the update as well as you can always log into WordPress and go to Appearance > Install Plugins to check for any potential updates and do them from there.