Thanks for asking.
Cornerstone is an essential tool to run X Theme as bunch of shortcodes are built into the page builder. When you load a page that's not designed with Cornerstone, only those components will load that required to run X Theme.
Cornerstone is not a resource hungry tool and won't slow down the performance of server and load time of website until and unless you are using heavy media files. However if you would like to optimize the load time, I suggest you to please take a look at our performance optimization guide: