CriticalCss: Defer unused CSS

The problem is elsewhere (and in my opinion not important); when you’re using “inline & defer” (potentially with the automated critical CSS plugin) the critical CSS is inlined and the full CSS is technically not deferred but “preloaded” meaning it is loaded without it being render-blocking (which is a separate GPSI recommendation). AO uses Filamentgroup’s loadCSS for this purpose.

The advantage of using “preload” is that the page below the fold is styled as soon as possible without the CSS being render blocking. If it would be deferred (as AO used to do a couple of versions ago) the chance was bigger that the user scrolled down to a part of the page that was not styled yet. Given the fact that preloading the full CSS does not block rendering, there is little advantage to be found in deferring it instead and the disadvantage might be significant.

hope this clarifies,
frank