Freeing up space · What's Using Space (Storage Inspector)
What happens when I click Move to fast drive in What's Using Space?
Short answer: A confirmation sheet shows the destination, size and any apps using the folder, with an optional auto-sync toggle. Confirm and a progress sheet tracks the move; the folder then keeps working from its original place.
A single confirmation sheet opens showing everything at once: where the folder is going, its size, and any apps currently using files inside it, with Quit and Quit all buttons and a Recheck. There's also an Auto-sync toggle that, when on, moves new files added to that folder later to your fast drive too.
Confirm and a live progress sheet shows how much has transferred, the speed, time remaining and each step. When it's done, the folder keeps working from its original place through links, and it appears in the Relocated panel with a Move back button.