APFS has this weird feature of purgeable space which is basically disk space that should be empty but is still reported as used. If anything tries to claim disk space it will be purged but for any reporting purposes the disk might look full.
So in case you always seem to be on the brink of running out of disk space you might want to run this (at your own risk of course :))
sudo /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs.util -P /System/Volumes/Data/private/var/db/*Note that this might take a while (few minutes) on a first run. Given that it might be deleting 100s of GB it makes sense.
As an example it looked like this for me:
$ df -h .
Filesystem Size Used Avail Capacity iused ifree %iused Mounted on
/dev/disk3s1 926Gi 846Gi 43Gi 96% 4057305 448723440 1% /System/Volumes/Data
$ time -p sudo /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs.util -P /System/Volumes/Data/private/var/db/*
request has flags: 0x0 type: 0x0 min_size 0 max_age 0 desired_amt 0 (size: 32)
Purging files on /System/Volumes/Data/private/var/db/Accessibility returned 0 (OK). Deleted amount: 303885606912
real 220.16
user 0.01
sys 55.53
$ df -h .
Filesystem Size Used Avail Capacity iused ifree %iused Mounted on
/dev/disk3s1 926Gi 563Gi 326Gi 64% 3657478 3415215200 0% /System/Volumes/Data
Subsequent runs are really fast though:
$ time -p sudo /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs.util -P /System/Volumes/Data/private/var/db/*
request has flags: 0x0 type: 0x0 min_size 0 max_age 0 desired_amt 0 (size: 32)
Purging files on /System/Volumes/Data/private/var/db/Accessibility returned 0 (OK). Deleted amount: 0
real 0.04
user 0.01
sys 0.02