20-25 % of JPEGs in the internet are progressive. MozJPEG outputs progressive JPEGs by default. Safari chooses not to show intermediate results, but they are a

20-25 % of JPEGs in the internet are progressive. MozJPEG outputs progressive JPEGs by default. Safari chooses not to show intermediate results, but they are available with Chrome and Firefox. The impact of progression on user experience is a complex question. It is for minimizing user experienced latency vs. (over)activating preattentive processing by images changing on the screen. Last year, Moritz Firsching (also the author of the blog post in question) made several improvements to the progression of traditional JPEG (libjpeg-turbo, Chrome, Firefox). Those changes -- in my opinion -- dramatically reduce the flicker and poor renderings that could occur from traditional JPEG progression, making progressive JPEGs more attractive overall.