A common problem people have been reporting is the inability to reformat an APFS drive as something other than APFS. It appears in Disk Utility that you can only erase a disk and keep it as APFS. However, a simple switch in Disk Utility is preventing you from selecting the device rather than the volume. Once you select the volume, you can reformat however you like.
If you need to take the extreme step of reinstalling macOS Sierra, you can do so using Recovery mode. You can choose to erase the drive and start fresh, or simply replace macOS and leave your documents and apps alone. This is handy for fixing extreme problems or before passing the Mac along to a family member.
If you are about to sell or give away an old Mac, it is important to erase it completely and reset it so it is exactly as it was when you first bought it. It is important to remember to sign out and remove all accounts and services first, then erase the drive, and then use Internet Recovery to install its original operating system.
Most off-the-shelf USB flash drives are formatted for Windows computers. You can easily reformat a drive to use the standard Mac OS Extended format with the Disk Utility app. Keeping the drive in MS-DOS format may be a better option, however, if you plan to use it on both Mac and Windows computers.
You can quickly and easily create compressed disk images from folders to archive projects. The resulting disk image saves space, reduces clutter and hides the files from searches. You can also encrypt the disk images to secure the files.
When you buy a USB Flash Drive, also called a Jump Drive, Thumb Drive, USB Stick or one of many other names, it usually comes formatted for Windows computers. If you plan to use the drive only for your Mac, then you can easily reformat it in Mac OS Extended format using Disk Utility. Flash Drives also sometimes come with specialized Windows software that Mac users don't need. Formatting cleans off these files to get it ready for you to use.
You can erase your Mac and set it up so it is ready for a new owner by using the recovery partition. This hidden part of your hard drive allows you to boot into a special mode where you can erase all of the contents on your Mac and re-install the system. There are a few things you should do first, such as logging out of iCloud and deauthorizng your account in iTunes. By using a special security feature of Disk Utility on the recovery partition, you can ensure that your data is erased.
Learn how to make copies of data CDs and DVDs using Disk Utility. With one optical drive in your Mac, you need to create a temporary disk image on your hard drive. Then use that disk image to create physical copies of your disc.