How Magento Defer Parsing of Javascript extension works
Defer Parsing of JavaScript is a Magento 1 and 2 extension that helps you remove render-blocking javascript from your pages.
What is render-blocking javascript? Find out on google helper page.
The extensions requires no configuration - once you install it it is ready to be used.
Disclaimer: it is a good security measure to backup your files and DB before you use the extension. Just in case things go wrong you would have all your data intact in a safe place.
Benchmarks
I run benchmarks with Google PageSpeed Insights:
With gtmetrix:
With webpagetest:
