Read this before continuing: Only use this for making more room if you need to change the partition size of your disk. Usually for installing Bootcamp or having multiple partitions on a drive. If you don’t understand the above, don’t do it! The method is not a way of getting more space. That is all handled by the operating system.
APFS – How a Smart File System Can Make Some Things Difficult
Because Apple has changed to a much smarter file system, my old method of creating a file and then duplicate that file until the disk was full, thus forcing Mac OS to start to remove the Purgeable portion of the drive doesn’t work anymore. That’s because APFS is smart enough to recognize that it’s the same file, so it makes pointers to the original data, so it doesn’t take up extra space. So here’s how to do it in Mac OS High Sierra.
Let’s Fill Up The Disk To The Brim To Remove Purgeable
Open the Terminal application in Applications/Utilities. What we need to do is to start making a file that will grow until the disk is full. So enter the following into the Terminal window:
The Disk Is Full, Let’s Continue.
When the Terminal window command ends with the message “No space left on device,” the disk is full, and mission accomplished. Mac OS should now have removed all the Purgeable space from the drive. So all that is left is to delete the file stupidfile.crap inside your home directory.
Don’t forget to empty the trashcan to regain the space.
You should now have no Purgeable part of the partition left.