Secondly and even more important, the native file systems of all major operating systems keep journals of all operations performed on the disk. For one, the FAT file systems do not support all properties and attributes of a file system designed for permanent storage. I do not recommend this for the permanent storage of my work.
I would always format an external disk to FAT32, as Mac OS has no problems reading and writing in that format, whereas a Mac formatted disk cannot be read by a Windows computer, which can be very unpractical.