Mac storage basics · Purgeable space and local snapshots
Why do local snapshots keep coming back after I delete them?
Short answer: Time Machine keeps creating them about hourly while it's on, and macOS makes one before updates. They expire on their own; there's no supported way to switch them off with Time Machine on.
Because Time Machine keeps making them on its schedule while it's turned on, roughly hourly, and macOS makes another before each system update. Deleting today's snapshots frees space now; new ones will appear and expire on their own.
There's no supported switch to stop local snapshots while Time Machine is on. That's usually fine: they're short-lived and macOS releases them when space runs low. If they're a problem right after a big clean-up or move, releasing them once is enough — Storage Studio's Local Snapshots window offers a one-click Reclaim for space a move has freed but snapshots still hold. See what local snapshots are.