&gt; Additionally, the reflow cost post-execute will be &lt;100ms<p>It really depends on the page.  It&#x27;s pretty easy to come up with pages that take a lot longer than that to reflow (tables, deeply nested flexboxes, etc).<p>I agree that typically making the script async is a good idea, but it&#x27;s really worth measuring both ways for the particular script and page in question.