To remove the data from a USB drive or any other drive completely.Here are some other factors that will conclude that formatting the external drive with Mac is necessary as it will also improve the performance of the drive. Unless you intend to use the drive for file exchange between Windows and Mac, the formatting would be the right thing to do. But unless you format the drive on Mac, it can't be used as a bootable disk or with Time Machine. It is possible to read and write on a drive that has a different file system. But if you want to ensure that the drive has complete Mac compatibility, then you'll have to format the drive using the Mac OS Extended filesystem. It is done as a routine maintenance task. Overview of Formatting Drive on Macįormatting isn't just a process of erasing the existing data on a drive. The Best Format Choice of External Drive on Mac