We love our Macs, and we love the files in there. Which makes it so distressing whenever we get the message that we’re running low on space. Due to how the Mac integrates storage space with its hardware, they needed to get creative with how this space was managed.
The biggest problem were the files themselves: how could the Mac OS safely distinguish which files are essential and which were not? So they took a look at user behaviour - what they put in the Mac, how long these files stayed in the system and how regularly they were accessed. In particular, they noticed that some files were occasionally accessed, they would be flagged as essential by the user and therefore not qualified for deletion.
It’s a lot like how we have junk and clutter lying around our rooms - keepsakes, mementoes, or things that we’d just plain forgotten about but don’t want to let go of. This is what a Mac’s “purgeable space” contains: files such as documents, photos, and videos that can be deleted in order to make more space.
This purgeable space is automatically calculated by the Mac OS and quietly downloaded in the background, storing these files online or in the cloud while you work. If you ever decide to purge this space, the files disappear from your computer but can be downloaded on demand whenever you may need them again, ensuring that a copy is present at all times - just not on your system itself, if you ever need more space.
Accessing this feature is easy: simply go to your Optimised Storage Recommendation (the path is usually [Store in iClouds/Optimise Storage/Empty Trash Automatically/Reduce Clutter]. Alternatively, there are several third party apps that can clear this space for you.
What is the point of showing this as free space? Simple: it gives you a more accurate idea of how much free space you actually have by showing the files that you can remove if you really need the date. With purgeable space, Mac users can have a realistic expectation of the amount of space available to them on their devices.