As I understand it, a round-trip request on a mobile network can be very expensive [0]. One of the ways that AMP enables sites to load instantly-upon-click is

As I understand it, a round-trip request on a mobile network can be very expensive [0]. One of the ways that AMP enables sites to load instantly-upon-click is by starting those requests in the background. (Then, when the user clicks, it's just a matter of bringing the IFRAME into view - no network involved.) Loading a traditional site can have side effects (e.g. reporting a view to an advertiser's analytics). By using the AMP validator, Google Search knows it's safe to preload and prerender an article, without triggering side-effects like analytics. So it's more than just loading faster than some threshold; it needs to be safe to cache and prerender the content. The AMP validator is what asserts these are both safe. (Note, I don't work on AMP and don't represent Google - this is my personal understanding.) [0] Ilya Grigorik's time-to-glass talk https://www.youtube.com/watch?v=Il4swGfTOSM https://www.youtube.com/watch?v=Il4swGfTOSM