CleanEject

When you connect USB-disks, camera's, GPS devices and similar to the Mac several invisible files and folders will be generated; when putting files on it several more invisible files will be created.

When you delete files, they are moved to the folder.Trashes still taking up disk space; to get rid of them you need to empty the Trashcan.
When the device is connected to a Windows PC the invisible files will be visible.