When a browser loads a resource from a third party server, the domain name of the server must be resolved to an IP address before the browser can send the request.
With this feature Swift Performance will tell the browser to resolve these domains early, before even the parser find them in the DOM.
It can speed up loading 3rd party assets, and navigating to 3rd party sites.
WordPress has this feature by default, however Swift Performance extends it, as it can find all domains in CSS not just in the HTML source.
You can also enable Collect domains from scripts as well. If you do, Swift Performance will collect 3rd party domain names from scripts as well. If you don’t, then Swift Performance will collect domains only from HTML and CSS.
If you find that some domains are unnecessary prefetched, then you can exclude it from prefetch DNS. You can use full- or partial domains here.