SharePoint 2013 Why document Preview Doesn't Work in Hover Panel

If you do not see the Document Preview in Hover Panel or Preview pane of a document in a library or in Search result you probably do not habe Office Web Apps (OWA) configured for SharePoint.

In SharePoint 2013 the Office Web Apps (OWA) is no longer a SharePoint Service Application and it needs to be deployed as a separate OWA farm.You can then establish a connection between the SharePoint Farm and the OWA Farm using the New-SPWOPIBinding and the Set-SPWopiZone powershell cmdlet.

The Office Web Apps Server is required in order to view Office documents in the Hover\Preview Panel. There are some good post around the web on how to configure and connect these two servers.