System data on Mini Mac 1

System Data, also referred to as "The Other Category" can not be altered, modified, move or deleted since it is part of the Mac’s operating system. Doing so would corrupt the OS and render the OS inoperative requiring a Wipe and Re-Installation.

The Other category is a potpourri of files which include:

• System temporary files

• macOS system folders

• Archives and disk images (.zip, .iso, etc. - often found in the Downloads folder)

• Personal user data

• Files from the user’s library (Application Support, iCloud files, screensavers, etc.)

• Cache files

• Fonts, plugins, extensions

• Other files that are not recognized by a Spotlight search

• Media files that cannot be classified by Spotlight as a media file because they are located inside of a package

They can be located anywhere on your hard drive. The files that you have control over are located in the Documents, Downloads, Pictures, Music and Movies folders.

System data volume will vary from day to day. There is little we can do to affect it significantly.

“System Data” (or “Other”) storage is an amalgam of files that don’t easily fall into the defined categories of “Audio" “Movies” “Photos” “Apps” and “Backups”.

You can’t directly manage the contents of this category. That is done by macOS. The category varies in size depending on the current state of your Mac.

What you can do…

• 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.

• Reboot your Mac at least weekly.

• 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 take up the most room are movies, images and music.

• Force Time Machine to delete local snapshots:

About Time Machine local snapshots - Apple Support

• Use Disk Utility to delete APFS snapshots:

View APFS snapshots in Disk Utility on Mac - Apple Support 

This from Apple on the subject of freeing up space:

Free up storage space on Mac - Apple Support

Also, please see the following guidance from Apple: 

Find and delete files on your Mac - Apple Support

That is correct. Such software is dangerous because it may remove system critical items and often causes other problems. We never recommend use of those cleaning apps.