A search result needs to be quick and easy to find and read - and on the same time display as much relevant information as possible to the end user. These two ambitions often conflict with each other - the more information you add to a result, the more "cluttered" the UI looks.  The more "cluttered" the UI, the harder it is to scan.

The hover panel is an exciting addition to SharePoint Online 2013 and introduces a nice balance between the quantity of information and the organization of that information.

We pared down our inline results to contain only key pieces of metadata common to most results, such as the title, URL, and hit-highlighted summary. These compact, streamlined results enable you to easily scan the page. Then, when you want to learn more about a result, you can hover your cursor over that result to see the hover panel dialog box.  The hover panel contains rich metadata that enables you to investigate a result more thoroughly, without having to click through and load the document.

In the hover panel we include an index of the section headings and slide titles that are inside of the document. We call these "deep links" and you can see them in the hover panel under the heading "Take a look inside". These headings and titles are links—clicking through will take you directly to that section (or slide) in the document!
The bottom of the hover panel contains a list of actions that may be performed on a result. You can follow or open the document, view the document's library, or send the document in an email message right from the results page.

Most prominent in the hover panel is the high-fidelity Web Application Viewer preview, available for all Office documents saved to SharePoint. These interactive previews are big enough to give you a solid idea of the structure, contents, and styling of the document you're hovering over. You can page through the document, view charts and tables, and even see the animations of a PowerPoint slide (If the Word preview text is a bit too small for you, here's a hint—double-click to zoom).

Its now very easy for you to judge search results, because you can quickly scan through an entire document to decide whether it's the one you are looking for.