Static CDN serving for "dynamic" websites
Static pregenerated websites behind CDN scale massively better than any php+mysql CMS (wordpress, drupal, joomla).
This has boosted a number of site generators like jekyll. But why now? Why not before?
Because most of the sites had a dynamic element that couldn't be regenerated easily. Comments, mostly.
A few dynamically generated sites have become static by the introduction of Disqus commenting system that sits into browser without any server-side integration. Getting the same level of integration at the server side would bring more complexities - depends on the frameworks, language and version compatibilities.
By keeping 3rd party components outside of your server walls your internal systems are better protected from being compromised.
On the other hand this risk is passed on to the end-user by being exploited to any code 3rd party chooses to run in her browser.
Power of insight
Browser always sees more about your user than your server because it's closer to the user. Being closer is better.
Browser era MVC
What are other less covered upsides and downsides of moving more action to the browser?