I'm struggling with a clogged internal HD on a late 2014 MacPro. Have cleaned out the cache and the usual trash-emptying, old app deleting, etc. After all that I restarted and had about 18GB freed up.
Have been using the computer for about an hour now, with the storage bar open. Now down to about 9GB available.
System data is nearly 160 GB (!!) but can't figure out how to get in there and see what's there to delete, but based on what I'm seeing, guessing some kind of aggressive automatic backup is happening.
This happens to me on my iPhone and iPads as well...not so often on my computers. Sometimes I can trace it back to mail programs like AOL, if I toss it out and restart, it returns to normal. when I reinstall it slowly creeps up again. Rarely does it seem to actually impact me.
It looks like it's about two years worth of local Time Machine snapshots. Bavcking up to cloud anyway, so turned TM off, but need to figure out how to delete the snapshots - preferably in bulk.
DaisyDisk is pretty good for this. Gives you a much more granular breakdown -- and lets you actually act on what you find by letting you trash stuff from within the app. Works better when you pick Scan as Administrator. Just be careful what you trash!
It looks like it's about two years worth of local Time Machine snapshots. Bavcking up to cloud anyway, so turned TM off, but need to figure out how to delete the snapshots - preferably in bulk.
Apple's Time Machine is an essential file backup tool for macOS, but it too has a backup that works off your Mac's primary drive. Here's how Time Machine's local snapshots work, and how to get rid of them if you want them gone.
appleinsider.com
[edit: just remembered another option, which is Carbon Copy Cloner. It will list out snapshots and let you delete them. If you don't already have it, pretty sure you could download a trial and do what you need.]