Mac storage basics · Disks, APFS and formats
Why do I need to eject a drive before unplugging it?
Short answer: Ejecting lets macOS finish writing and close the drive cleanly; unplugging without it can lose recent changes or damage the drive. Quit apps using it first.
Ejecting tells macOS to finish writing any pending data and close the drive cleanly. Unplugging without ejecting can lose the last changes or damage the file system — macOS warns with Disk Not Ejected Properly.
Eject from Finder's sidebar (the ⏏ button), by dragging the drive to the Trash, or with Command-E. If macOS says the disk is in use, quit the app that's using it first. Storage Studio has its own eject confirmation that pauses its work and tells you what's still using the drive — see external drives.