Firstly, the new "Preview" Feature in serach results is called "Hover panel". With Hover panel each result is quick and easy to find and read.

When you search something, In the results it contains only key pieces of metadata common to most results, such as the title, URL, and hit-highlighted summary. These compact, streamlined results enable users to easily scan the page. Then, when the user wants to learn more about a result, they can hover their cursor over that result to see the hover panel dialog box.  The hover panel contains rich metadata that enables users to investigate a result more thoroughly, without having to click through and load the document.Some important metadata displayed in the hover panel - file type, the date the result was last edited, the people who have edited it recently, and view counts (so you can see how often a document was viewed).
In addion to the Metadata it also displays Section headings and slide titles that are inside of a document, under the heading "Take a look inside. These are called "deep links" and you can see them in the hover panel. Even cooler, these headings and titles are links—clicking through will take you directly to that section (or slide) in the document! Now, users can search across millions of documents, and with a single click, zoom right in to one specific section of one document.