Troubleshooting & messages · Free space and clean-up messages
Why does it warn that clearing something can't be undone because there isn't room for a copy?
Short answer: There's nowhere to keep a recoverable copy, so clearing this would be permanent. Connect your fast drive to keep it recoverable, or confirm only if you're sure.
Normally what Storage Studio removes goes to the Recycle Vault so you can get it back. When there's no room anywhere to keep that copy — your fast drive isn't connected and the space on your Mac is too tight — clearing it would be permanent, so it asks you first.
Connect your fast drive to keep removals recoverable, or confirm only if you're sure you won't need it.