Formatting a drive will delete all of the data on it and create a new file system. You'll need to format a drive in order to install Windows on it or to start using it if you're installing an extra drive. You can format a drive to quickly erase all of the data on it. You can also shrink existing drives and format the remaining free space to create a second drive on your computer. If you are disposing your computer you can use special tools to securely erase all of your data.