Usually, each time you install a new application it is registering it's own filetype. But not all of them remove it from the registry when you are uninstalling it. Also you can simply remove the application from the hard disk but registry remains unchanged. This tab helps you delete such "lost" filetypes from the registry. Find title of filetypes in the list that are belongs to non-existent application (usually it has no icon) and remove it from the list.