Freeing up space · Local snapshots and held space
What does Delete all backed-up do in Local Snapshots?
Short answer: It deletes every snapshot already backed up to Time Machine in one step, after a confirmation. Local-only and system-required snapshots are always skipped.
It removes, in one step, every snapshot that's already safely backed up to Time Machine — the ones with the green check. Snapshots that exist only on this Mac, and those macOS requires, are always skipped, even here.
It asks you to confirm first, a failure on one snapshot never stops the others, and the window stays responsive while it works. The result appears in the outcome banner at the bottom. To free a specific amount instead, use Custom reclaim.