Yes you will be able to reformat it and add files to it after ! Bootable usb, you can boot windows 8, windows 7 installation with it .. Etc.. If you put your ISO on it with a software it will make a bootable USB !
"Definition of:bootable disk. bootable disk. A CD-ROM or DVD-ROM that contains its own operating system ready to load. PCs are typically configured to look for the OS on a CD or DVD first and then the hard disk. Newer machines can also boot from a flash memory-based USB drive (see USB drive)."
Same thing as a CD/DVD !