In reply to Raul.

“It was a feature that existed as an option on wp-admin (disabled by default), for developers to test the impact of the “specified scripts”, fonts, or ajax requests on performance, but without impacting real user experience.”

I believe, and I have asked the Twitter poster 3 times now for his methodology and he has avoided a straight answer, that this is also ONLY is the option is set and a script specified in WP Optimize.

I am happy if someone proves me wrong and demonstrates how teh code can be triggered without user knowledge.