Oh The Scripts We'll Load by Tim Kadelc

This in-depth analysis of loading scripts in the browser is filled with nerdy technical details.

For example, Tim tells this story about a team that was loading a giant bundle of JavaScript using the <script async> tag. To try and improve performance, they ruthlessly cut down the amount of JavaScript being shipped to the browser. They got the file size way down and...performance got worse! Do you know why? Watch this video to find out—or I’ll just tell you why: even though it was async, the giant mass of JavaScript was blocking the parser when it arrived, and because it was so much smaller than before, it was arriving earlier and thus blocking the parsing of the HTML document earlier and giving the appearance of slower performance. Hence Tim’s statement at one point in his talk:

Don't take anything as gospel. There will always be tradeoffs.