Most web pages have suboptimal designs and dependency downloads. This system speeds things up by changing the order of dependencies such that the pages can be rendered more quickly.
If you do it manually, you can generally do things that will speed things up more significantly, but that requires time, specialized knowledge, and attention to a not very glamorous area of web development.
An example might be an image that shows up on a hidden tab that does not have enough information in the html for the browser to understand it is not a required element for initial rendering. If the request for that image can be pushed to the time frame after the initial render the end user has a better experience.
When the web was limited to 28K speeds for a significant amount of the userbase people paid a lot more attention to these kinds of things. Now that a significant amount of end users have broadband speeds, web developers are more concerned about other things because some things as simple as leveraging a CDN and outputting appropriate cache control headers are enough optimization to provide adequate performance.
It's not clear on my initial read if this is a new rendering engine, a client side script, or a server side parser that re-shapes output, but the intention is obvious - download things in the right order to get the fastest page load times. I've done this kind of optimization before and it can make an enormous difference - especially with bandwidth challenged end users.
It changes the page fairly dramatically. Before rolling out a page, you run it through their parser, which creates skeletal html and a javascript stub which you serve in place of the original html.
Then, when this substituted page is loaded, their javascript rebuilds the original web page with calls to eval() and whatever.innerHTML, in a way that the dependencies are supposedly streamlined.
Doesn't this describe all web browser development of the past 15 years?