How to Use Optimize Storage on a Mac (and Its Limits)

In short: macOS has built-in tools to free up space, and they work well for a few specific jobs. But Optimize Storage does not clean everything, and it is worth knowing where it stops. Here is how to use it and what it will not do.

If your Mac is running low on space, macOS has a built-in feature that can help before you reach for anything else. Apple groups these tools under Storage settings, and one of them is literally called Optimize Storage. It is genuinely useful, it ships with the system, and it costs nothing. It also has real limits, and knowing those limits saves you from expecting more than it delivers.

This guide walks through how to optimize Mac storage using what Apple already gives you on macOS Sonoma (14) and Sequoia (15), then shows where those tools stop and what to reach for when they do.

Where the built-in tools live

Open the Apple menu, choose System Settings, then click General in the sidebar and select Storage. You will see a colored bar that breaks your disk down by category (Applications, Documents, macOS, System Data, and so on). Give it a moment to calculate, since the numbers settle as it scans.

Below the bar is a list of Recommendations. This is where Apple's optimization options actually live, and each one does a different, specific thing:

• Store in iCloud moves older files, photos, and messages to iCloud and keeps lightweight local copies. You only download the full version when you open it. This needs enough iCloud space and an internet connection.
• Optimize Storage (the named option) removes Apple TV movies and shows you have already watched, and trims some email attachments. It is narrower than the name suggests.
• Empty Trash Automatically deletes items that have been in the Trash for more than 30 days.
• Reduce Clutter opens a window to review large files, downloads, and unsupported apps by hand.

What actually frees up space

In practice, the biggest quick wins come from a few places. Click the small info icons next to categories like Documents and Applications to see large files and installed apps sorted by size. Sort by size, look for things you genuinely no longer need, and remove them one at a time.

The Developer and System Data categories are often the confusing ones. System Data holds caches, logs, and support files that macOS manages itself. You generally should not go digging inside /System or system-owned folders to shrink it, and you should never delete files inside /System. Much of System Data clears on its own over time or after a restart.

One honest note about deletion: emptying the Trash is permanent. Anything you drag out of Storage settings and into the Trash can be recovered right up until the Trash is emptied. So before you empty it, take one last look. That reversible window is your safety net, and it is worth using deliberately rather than clearing on reflex.

The limits worth knowing

The built-in tools are good at a handful of tasks and silent on the rest. Here is where they stop:

• They do not clear application caches, browser caches, or leftover support files from apps you have uninstalled.
• They do not find duplicate files or large old downloads for you automatically; you review those by hand.
• Store in iCloud does not free space so much as move it. Your files still exist; they just live in the cloud, and you may pay for that storage.
• The Optimize Storage option is limited to Apple TV content and mail attachments, which may be nothing at all on your machine.
• Uninstalling an app by dragging it to the Trash usually leaves behind preference files, caches, and support folders in your Library.

None of this makes the built-in tools bad. They are a sensible first pass. But if System Data is huge, or you have years of app leftovers, you will hit a wall the built-in tools were never designed to break through.

When you need a dedicated cleaner

If the built-in pass is not enough, a good third-party cleaner picks up caches, logs, and orphaned app files that macOS leaves alone. The important thing is choosing one that respects the same safety principles you would use by hand: it should show you a preview before removing anything, default to touching only user-level junk (not system files), and send removals to the Trash so you can undo a mistake instead of losing files permanently. A cleaner also has no reason to phone home; if you want to confirm that, a firewall like Little Snitch will show you exactly what it does and does not send.

On those criteria, our top free pick is CoreSweep: free forever, with an optional one-time Pro upgrade ($49, no subscription), zero telemetry, and reversible Trash-based deletes. A strong best-value runner-up is SkoonMac, which is also free with a one-time $19 Pro tier. Either one complements the built-in tools rather than replacing your judgment.

A simple routine

Start with Storage settings. Empty the Trash on old items, review large files and apps by hand, and let System Data settle after a restart. If you still need space, run a cleaner that previews first and deletes reversibly. Do that a couple of times a year and you will rarely see a full-disk warning again.

Frequently asked questions

Does Optimize Storage on a Mac actually delete my files?

The named Optimize Storage option is narrow: it removes Apple TV movies and shows you have already watched and trims some email attachments, which may be nothing at all on your machine. The related "Store in iCloud" option does not delete files either, it just moves older files, photos, and messages to iCloud and keeps lightweight local copies. So the space you gain from these tools is limited, and your files stay available rather than being permanently erased.

Why is System Data so large on my Mac, and can I delete it?

System Data holds caches, logs, and support files that macOS manages itself, so it can look surprisingly large. You should not go digging inside /System or system-owned folders to shrink it, and you should never delete files inside /System. Much of System Data clears on its own over time or after a restart, so it is usually best to leave it alone.

Do the built-in macOS tools clean up app caches and leftover files?

No. The built-in Storage tools do not clear application caches, browser caches, or the preference and support files left behind when you drag an app to the Trash. For that you need a dedicated cleaner, and the safe ones show you a preview before removing anything, touch only user-level junk rather than system files, and send removals to the Trash so a mistake stays reversible.

← All Mac cleaning guides · Back to the comparison