The big idea is that if you can cut down the number of network requests the browser makes to see if the images and other resources it cached the first time you went to a site are still valid you can speed things up rather a lot.
Writing in his bog, Google engineer Takashi Toyoshima said that users typically reload pages because they either look broken or because the content looks like it should have been updated. When browser developers first added this feature, it was mostly because broken pages were common. Today, users mostly reload pages because the content of a site seems stale.
Google simplified Chrome’s reload behavior and it now only validates the main resource. Facebook, just like other pages, says its pages now reload 28 percent faster, too.
Google admits that is a very minor change but the effects aren’t so minor. They estimate that the new method reduces the number of validation requests by as much as 60 per cent, making pages reload 28 per cent faster. And the sooner the browser finishes reloading a page, the sooner it can stop using data and hardware resources.