It is used to audit your media basically. It will show you your games and some of the more common media types like 3D Box, Box Front, Music, Videos, Manuals, etc. and let you know how many you have of each so you can easily see if things are missing in a way.
Just click on a platform then go to >Tools>Audit this Platform and it will run then it pops up a view like Excel. You can highlight all or some and copy paste into Excel.
Have you synced your collection to the database from within LaunchBox?