With the Hybrid Placeholder it's possible to load heavy parts of a Rendering Contents Resolver later. When a user navigates to a page directly everything will be loaded (with SSR support). When a user navigates to a page using Client-Side Rendering with XHR (single page app) the data is fetched with the layout service. Than the heavy parts can be skipped and will be loaded once the page is already visible.
Last year I wrote a blogpost about the Hybrid Placeholder for Sitecore JSS. In that blogpost there are some code snippets on how you can implement the Hybrid Placeholder by yourself. Since then I have made some improvements and now it's also released as an open source package.
You can download the Hybrid Placeholder here: https://github.com/jbreuer/Hybrid-Placeholder
I've also made a getting started video on how to install and use the Hybrid Placeholder: https://youtu.be/-8k7jzuRk9U