Turning on iCloud's storage optimization feels like the obvious fix when your Mac's drive is nearly full. But many users flip the switch, wait, and find the needle barely moves — or watch "store in iCloud not working" pile up in search queries. Understanding what iCloud actually offloads, where it stops, and what sits permanently on your local drive is the difference between a Mac that breathes again and one that stays perpetually short on space.
What "Manage Mac Storage With iCloud" Actually Does
macOS has two distinct iCloud storage controls, and they are often confused:
- Optimize Mac Storage (under System Settings → Apple ID → iCloud → iCloud Drive) — when local storage runs low, macOS automatically removes the local copies of older iCloud Drive files and keeps only lightweight placeholders. The files still exist in iCloud; clicking one re-downloads it on demand.
- Optimize Storage (under System Settings → General → Storage → Recommendations) — a broader setting that also removes iTunes and Apple TV movies you have already watched, plus older email attachments. Separate from the iCloud Drive toggle above.
Both settings are reactive: macOS decides when and which files to evict based on available space and recency of access. You cannot force-evict a specific file this way.
How to Enable Optimize Mac Storage
- Open System Settings (macOS 13 Ventura and later) or System Preferences → Apple ID (macOS 12 Monterey).
- Click iCloud, then iCloud Drive (or the "Options…" button next to it).
- Enable Optimize Mac Storage.
- Separately, go to System Settings → General → Storage and review the Recommendations panel. Enable Optimize Storage if you want watched video and email attachments removed too.
Once enabled, macOS will begin evicting eligible iCloud Drive files in the background. You can check which files are local versus cloud-only in Finder: cloud-only files show a small download icon next to their name.
Where iCloud Offloading Falls Short
iCloud's optimization is genuinely useful for Documents and Desktop files. It falls short in several common situations.
It only moves files you store in iCloud Drive
Photos in iCloud Photos Library, documents in iCloud Drive, and Desktop/Documents folders (if you have enabled Desktop and Documents syncing) are eligible. Everything else — applications, system files, caches, game data, browser profiles — stays local regardless of your iCloud settings.
The "System Data" category can balloon without iCloud touching it
Open System Settings → General → Storage and you will likely see a large "System Data" slice. This category contains application caches, log files, temporary files, Spotlight indexes, Time Machine local snapshots, and purgeable space. iCloud does not touch any of it. On a busy Mac it is common to see 20–40 GB locked here.
App leftovers accumulate invisibly
When you drag an app to the Trash, macOS removes the .app bundle but leaves behind preference files, caches, crash logs, and support data scattered across ~/Library/Application Support/, ~/Library/Caches/, ~/Library/Preferences/, and /Library/. These never leave your drive, no matter how aggressive your iCloud plan is.
Duplicate files are yours to find
iCloud syncing can actually create duplicates if you have multiple Macs or if a sync conflict occurs. The resulting duplicate files sit on local storage; iCloud has no mechanism to deduplicate them for you.
Why "Store in iCloud" Stops Working
If you enable Optimize Mac Storage and space does not free up, the most common causes are:
- Not enough of your data is in iCloud Drive. If your large files live in ~/Downloads, ~/Movies, or external paths not synced to iCloud, there is nothing for macOS to evict.
- macOS does not consider space "low enough" yet. The threshold is not published, and on SSDs with larger capacities macOS can be conservative.
- Local snapshots are inflating the used-space figure. Time Machine keeps hourly local snapshots; run
tmutil listlocalsnapshots /in Terminal to see them. They are purgeable and macOS should remove them under pressure, but they inflate the reported used space. - System Data caches are the real culprit. If you see 15+ GB in System Data, that is almost certainly the larger problem — and iCloud cannot help with it.
What iCloud Can Never Clean: Local Caches and Logs
The files that accumulate fastest on a working Mac are the ones iCloud ignores entirely:
| Location | What lives there | Safe to delete? |
|---|---|---|
~/Library/Caches/ |
Per-app cache files: thumbnails, compiled assets, network responses | Generally yes — apps rebuild caches on next launch |
/Library/Caches/ |
System-wide and daemon caches | Mostly yes, though some require a reboot to regenerate cleanly |
~/Library/Logs/ and /var/log/ |
Application and system log files | Yes — logs are diagnostic data, not required for operation |
~/Library/Application Support/ |
App data, databases, saved state — mixed | Caution — contains both safe leftovers and live app data; inspect before deleting |
/private/var/folders/ |
Temporary files, per-session data | Yes, but macOS cleans most of this on reboot |
You can manually clear your user cache from Terminal:
rm -rf ~/Library/Caches/*Note: This is permanent. Close all applications before running it, and be aware that some apps (notably Xcode, browsers, and Homebrew) store data in their cache folders that you may want to keep. Inspect the folder in Finder first if you are unsure.
A Practical Workflow: iCloud + Local Cleanup Together
- Enable Optimize Mac Storage for iCloud Drive — this handles your documents and keeps them recoverable.
- Check Storage → Recommendations in System Settings and act on anything listed (large files, old Downloads, watched video).
- Inspect System Data. If it is above ~10 GB, caches and logs are the likely driver. Clear
~/Library/Caches/manually, or use a tool that handles this safely. - Remove app leftovers from apps you have already deleted. Check
~/Library/Application Support/for folders whose parent app is gone. - Look for duplicates in your Downloads and Documents folders — iCloud sync conflicts can leave
(1)copies behind.
Steps 3–5 are where a native tool earns its keep. Crumb was built specifically to handle the local side of this: it clears system and user caches, logs, and temp files in one pass, finds leftover files from uninstalled apps, and includes a treemap so you can see exactly what is taking up space before you delete anything. Its "Is this safe to delete?" AI explains any unfamiliar folder in plain English, which is useful when you are unsure whether something in ~/Library/Application Support/ is a live database or a safe orphan. If you want to give it a try, you can download Crumb and run one free cleanup to see how much is recoverable.
The Honest Trade-off
iCloud offloading is not cleaning — it is deferring. Your files move to Apple's servers and come back when you need them; your total iCloud storage bill goes up as your Mac's local usage goes down. It is a genuine trade-off worth making for documents you access occasionally, but it does nothing for the caches, logs, and app detritus that grow continuously on every Mac. The two approaches are complementary: use iCloud to keep important files accessible from any device while keeping local storage tidy, and handle the local layer separately with deliberate, targeted cleanup.
Neither approach is risky when done with care. The main rule: before deleting anything outside of a known-safe cache folder, understand what it is. Permanent deletions from ~/Library/Application Support/ can break apps; those from ~/Library/Caches/ almost never do. When in doubt, move to Trash and wait a week before emptying it.