Apple's storage breakdown (Settings → General → Storage) shows a category called "System Data" or "Other" that can balloon to 50–100GB with no clear explanation. It isn't one thing — it's a catch-all for caches, logs, iOS device backups, disk images, and application support files that don't fit Apple's other categories. Deleting the wrong thing here can break apps, so go in this order.
01Start with the safest, biggest wins: caches
Caches regenerate automatically, so clearing them is low-risk.
- Open Finder, press
Cmd+Shift+G, and go to~/Library/Caches. - Sort by size. Anything belonging to apps you don't use daily can be deleted safely — the app will just rebuild what it needs.
- Leave folders for apps you use right now (like your browser) alone unless space is critical; deleting them won't break anything, but you'll lose logged-in sessions and speed until they rebuild.
02Check for old iOS backups
If you've ever backed up an iPhone or iPad to this Mac via Finder, those backups can be 10–40GB each and are easy to forget about.
Finder → iPhone device page (when connected) → Manage Backups, or check ~/Library/Application Support/MobileSync/Backup directly. Delete backups for devices you no longer own or have replaced.
03Find oversized disk images and installers
Downloaded .dmg installers and old virtual machine images are a frequent hidden cause.
find ~/Downloads -name "*.dmg" -size +500MRun this in Terminal to list any installer over 500MB sitting in Downloads — these are safe to delete once you've installed the app.
04Check Application Support for old, uninstalled apps
Uninstalling an app on macOS by dragging it to the Trash does not remove its support files.
ls -lhS ~/Library/Application\ Support | head -20This lists the largest folders in Application Support. If you see a folder for an app you uninstalled months ago, it's safe to delete that specific folder.
05Use the built-in Storage Management tool for a full picture
Settings → General → Storage → the small "i" button next to System Data (or the "Manage" button on older macOS) gives a categorized breakdown that's more accurate than Spotlight-based third-party cleaners.