Optimized Gutenberg Loading is an experimental feature designed to improve performance by decreasing the time it takes for a page to load. As an experimental feature, you will need to turn it on in order to use it. For more details about activating experimental features, see What are Elementor experimental features?
Gutenberg is the default editor of WordPress and is compatible with Elementor. When users create their sites using both Elementor and Gutenberg, the Gutenberg scripts and styles need to load every time the site renders a page. This slows down the page loading time.
Optimized Gutenberg Loading intelligently decides when these scripts and styles need to be loaded and which ones need to load. This should significantly speed up site loading.