Embedded resources include all CSSs, JSs, Images and other resources that are part of a landing page. By downloading all embedded resources of each landing page, the response time of each landing page will be the total sum of response times for all embedded resources.
Disable this option if you want a request to be made only to the URL of the landing page and not to retrieve the embedded resources.
For example in case you are using a Content Distribution Network or smart caching of any sort for the static content, you should disable this option.
If you don't know if this is important to you or not, ignore it altogether.