When a Mac says the disk is almost full, the space is rarely in one place. It is spread over caches, old downloads, developer tools and files from apps you no longer use. Here is where to look, in the order that usually gives the most back.
1. Find out what is actually large
Open System Settings, General, Storage. It shows broad categories, but not which folders inside them are large. To see that, you need a tool that sizes every folder at once, such as DiskAtlas, or Finder’s “Calculate all sizes” option in list view, folder by folder.
2. Downloads and disk images
Installers (.dmg, .pkg, .zip) stay in Downloads long after you installed the app. Sort
Downloads by size and remove what you no longer need. This is usually safe and often large.
3. Caches apps can rebuild
Apps keep caches in ~/Library/Caches. Clearing them is safe in the sense that apps recreate
what they need, but the space comes back as you use the apps again. Clear caches for apps you
no longer use first.
4. Developer tools
If you use Xcode, ~/Library/Developer can hold tens of gigabytes: build output
(DerivedData), simulators for old iOS versions, and device support files. Build output is
rebuilt on the next build. Old simulator runtimes can be removed from Xcode’s settings.
5. Files left by deleted apps
Dragging an app to the Trash leaves its support files in ~/Library/Application Support and
~/Library/Containers. Remove the folders that belong to apps you have uninstalled.
What to leave alone
Do not delete folders inside /System or /Library by hand, and do not remove anything you
do not recognise without checking what created it. Move things to the Trash first rather than
deleting them outright, so you can change your mind.
