Moving folders · How moving folders works
What should I not move to an external drive?
Short answer: Keep on your Mac anything you need with the drive unplugged, folders an app is still writing to, browser profiles and app data holding sign-ins, and macOS system folders. What's Using Space only offers a move where it's safe.
Keep anything you need when the drive is unplugged, anything an app is writing to right now, and folders that hold an app's sign-ins and settings. Moved files are only reachable while the drive is connected.
In practice that means:
- Work you need on the go if you often travel without the drive.
- Folders in active use — a project mid-build or a folder a sync app is still writing to. Storage Studio checks for recent writes and holds the move.
- Browser profiles and app data with sign-ins — Storage Studio leaves these alone because moving them would sign you out and break when the drive is away.
- macOS system folders — Storage Studio doesn't offer to move them.
When in doubt, use What's Using Space: it only offers Move to fast drive on folders it can move safely.