Select this option, all custom code like HTML, Javascript, PHP etc added to the Head and Body sections and the HTML Source elements will be excluded from the generated page for previewing. This can be used to check whether the incorrect rendering of the page is caused by invalid code added to those places.
Selecting this option will open the Preview Website Files in Local Web Server Dialog. Use this option to preview a website published to a directory on your computer. This is needed because some code on a page needs to be loaded from a web server in order to display the page correctly on web browsers.