tl;dr:Download & execution time are primary bottlenecks for loading scripts in 2019. "Aim for a small bundle of synchronous (inline) scripts for your above-the-fold content with one or more deferred scripts for the rest of the page."
tl;dr:(1) Lighthouse supports Performance Budgeting (2) Native image and iframe lazy-loading comes to the web (3) Google Fonts now supports font-display as a query parameter.
tl;dr:New loading attribute for images and iframes helps content load quicker, reduces network data usage and reduces memory usage. It should be shipped as part of Chrome 75.