We can depend on results generated by Gtmetrix or Google PageSpeed Insight to measure how well the site is performing.
Effectively defer Iframes embedded on websites
When these iframes are embedded on your site, the browser simultaneously loads Magento JS files of these pages, which can slow down your webpage.
Hence, using this defer js extension, there is no need to worry about the impact of external Iframes processing on your site performance anymore.
Raise your ranking on SERPs
Google indicated that site speed is used in ranking a website on both desktop and mobile searches.
How Can Magento 2 Require JS Improve Website Performance?
The browser often loads codes from the top to the bottom of the page, it has to load the content of all <script> tags, which adds additional time to load the web page.
Along with Full Page Cache, Magento 2 minify JS extension is an effective tool for speed optimization.