Optimize and page load speed
Optimize has minimal effect on the time it takes for your site pages to load. The time it takes for a page on your site to load, or latency, is mostly dependent upon the visitor's/user's connection speed. The primary source of latency is often the process of the browser connecting to the appropriate domains. As a result, users on slower connections may experience delays, while most users on a cable-or-better connection do not.
How Optimize minimizes latency
You'll find that pages generally load as quickly with Optimize as they do with other testing solutions, even those solutions that use a static content delivery network (CDN). Because Optimize is served from the same domain as Google Analytics, a DNS lookup and initial connection are seldom required. This reduces, often by as much as 50 percent, the amount of time required for the browser to request the page.
Optimize excels in low latency when you run a large number of concurrent experiments. This is because Optimize’s response is dynamic; the server performs much of the targeting and content pruning work with a single call to Google’s servers, which minimizes download sizes.
For example, if a test is targeted based on geolocation, Google Analytics audiences, or device type rules, those rules are all evaluated on Google’s servers, removing experiments and reducing download sizes when a user does not match a criteria.
Additionally, experiment inclusion and variant allocation are decided server-side, removing all content that the user is not randomly assigned to. This further reduces download sizes, particularly for sites running large numbers of tests and experiences. Instead of downloading every experiment and variant, Optimize only delivers what a user would be likely to actually see.
Page hiding and the timeout feature
Optimize provides advanced controls over the application and rendering of experiments. The Optimize page-hiding snippet enables you to temporarily obscure the page as changes are applied to prevent page flicker. Furthermore, the page-hiding snippet supports a configurable user timeout that lets you to set the maximum length of time that your page is hidden and a time after which experiments shouldn't be applied. Learn more about customizing the Optimize page-hiding snippet on the Google Developer website.