APFS guides.
How APFS counts space on a Mac, and why disk tools disagree about sizes: clones, snapshots and purgeable space.
System Data on Mac: What It Is and How to Shrink It
System Data is the catch-all category in Mac storage settings: logs, caches and swap. What Apple counts in it, what is safe to shrink, and what to leave alone.
StorageBeginnerAPFS
Purgeable Space on Mac: What It Is and How to Free It
Purgeable space is storage macOS can clear by itself, such as Time Machine snapshots and caches. How to see it, why it can block a copy, and how to free it now.
APFSStorageTroubleshooting
How to find large files on a Mac (and why the sizes lie)
How to find large files on a Mac, by size bracket, and why sparse files, APFS compression and hard links make Finder's numbers wrong.
StorageAPFSDeveloper
What is actually taking up space on your Mac
The ten places Mac storage actually goes: Xcode, Docker, iOS backups, Photos, node_modules, Mail, caches and snapshots, with what is safe to remove.
StorageBeginnerDeveloperAPFS