Freeing up space · Emergency Space
Can I keep using my Mac while Emergency Space is freeing space?
Short answer: Yes. It runs in the background, so you can close the window and work; reopen Emergency Space and press Show progress to check on it. Your own work gets the disk first.
Yes. Emergency Space runs as a background job, so you can close the window and carry on; reopening it gives you a Show progress button to return. It's built to stay out of your way while it runs — your own work gets the disk first.
If an app needs to be closed for a folder to move, you'll be asked first rather than having it closed for you. When it's done, you can see what came back in the What actually happened view. See Show progress.