If your Mac's disk quietly loses tens of gigabytes and Storage settings insists nothing big is installed, the most common hidden eater is Time Machine local snapshots — hourly APFS snapshots taken even when no backup drive is connected.
APFS snapshots let Time Machine keep hourly "undo points" on the internal disk. macOS is supposed to prune them automatically when space runs low, but large file churn (AI models, Docker images, VM disks — the exact workload of an AI-tool power user) can keep snapshots pinned and expensive for days.
tmutil listlocalsnapshots /
# each line: com.apple.TimeMachine.2026-10-15-091234.localSnapshots don't report a size individually — measure the delta instead: free space before and after deletion, or compare df -h / now versus after.
# delete one snapshot by exact name from the list above
sudo tmutil deletelocalsnapshots /com.apple.TimeMachine.2026-10-15-091234.local
# or thin all snapshots to the most recent few (supported on recent macOS)
sudo tmutil thinlocalsnapshots / 999999999999 4Deleting a snapshot only removes those hourly undo points — your actual Time Machine backups on the external drive are untouched. Worst case: you lose the ability to roll back files to a specific hour.
If you don't use Time Machine at all, simply turn it off (Settings → General → Time Machine). If you do use it but want fewer local snapshots on a laptop with a small disk, run backups more often to the external drive — the local snapshot cadence follows it. Developers with heavy churn (Docker, model downloads) can also exclude those folders from backups entirely, which reduces churn-driven snapshot growth: see our Docker disk guide for the companion cleanup.
Snapshots are one of the four classic hidden eaters, alongside developer caches, AI-tool data, and old iOS backups — the full triage order is in the System Data breakdown. For a visual once-over, DaisyDisk shows snapshots as a "purgeable" wedge and pairs nicely with the terminal workflow above; MacCleaner PRO automates the same thinning.