How can I reduce massive system data storage on my MacBook?

Hi,

"System Data" balloons on a Mac when app caches, logs, Time Machine snapshots, or leftover update files accumulate. You can safely reclaim this space by clearing user cache folders, deleting old local backups, and removing unnecessary files from the hidden Library folder.

Caches are temporary files designed to help apps load faster, but they can easily bloat to hundreds of gigabytes over time.

1) Open Finder.

2) Press Command + Shift + G to open the "Go to Folder" window.

3) Type ~/Library/Caches and hit Enter.

4) Look for folders with unusually large sizes (especially for Adobe, Spotify, or web browsers). To check sizes, select a folder and press Command + I.

5) Move the large, unnecessary cache folders to the Trash and empty it

Delete Local Time Machine Snapshots

Even if you don't actively use Time Machine, macOS frequently saves local backups in case you get disconnected from your backup drive.

1. Open Terminal (via Spotlight or your Utilities folder).
2. Type tmutil listlocalsnapshots / and press Enter to see a list of snapshots.
3. To delete a snapshot, type sudo tmutil deletelocalsnapshots <snapshot_name> (copy and paste the snapshot name exactly as it appears) and press Enter.
4. Enter your admin password when prompted.

Clear App Leftovers and Installers

If you delete apps, their preferences and support files are often left behind.

1. Go to the Apple menu > System Settings > General > Storage.
2. Click the "i" (Info) buttons next to categories like Applications or Documents to view specific files.
3. Remove old .dmg installer files sitting in your Downloads folder, as these are often counted as System Data.
4. Consider using a dedicated cleaning utility like CleanMyMac or the like utilities to safely find and remove system junk automatically in one click.

As you may have surmised, directly manage the contents of system data is fool's errand, and is something that is done by macOS. The category varies in size depending on the current state of your Mac.

Here are some things you can do to create more free space:

• Reboot your Mac at least weekly. Let the OS do housekeeping and clear caches.

• Empty the Trash in the Dock. 

• Empty the trash in the Photos app.

• Delete unused and unneeded application installers from your downloads folder and desktop. No need to store on your Mac what you can freely download any time.

• Transfer files that you don’t use daily to an external drive and then delete them from the startup drive and empty the trash. Files that typically take up the most room are movies, images and music.

This from Apple on the subject of freeing up space:

Free up storage space on Mac - Apple Support

Also, please see this guidance from Apple: 

Find and delete files on your Mac - Apple Support

Also, please see this user tip: How to Use Finder to Clear “System Data" on a Mac  (Thank you, @TheLittles!)

If you have enabled Time Machine to back up your Mac automatically and do not keep your backup drive connected all the time, then MacOS keeps a number of Time Machine snapshots on the drive as part of the backup process.  These TM snapshots can occupy a significant amount of drive space. You can disable the creation of these many TM snapshots by setting TM to backup manually rather than automatically at intervals.

You can view and manage these in Disk Utility or in the Terminal app.

View APFS Snapshots in Disk Utility on Mac - Apple Support