Because of the ironic breach, the bigger the better the hardware trend, the Mac hard drives are smaller than they have been for years. Thanks to expensive SSDs, the new Mac now has a low base of 128GB. In this sense, macOS Sierra includes new features designed to optimize hard disk space.
To optimize storage, the operating system scans the contents of the user’s hard drive and sorts the files into two camps: “purgables” and everything else.
What does “clean” mean?
“Purgable” describes files that macOS has decided to delete if necessary. This is similar to deleting data from your hard drive: the data is marked as spam, but it will not be lost until it is replaced. The data to be cleaned still exists as actual, available files, but macOS has considered these files consumable.
At this time, it is not possible to see exactly which files the operating system has marked as purgable. Also, you can’t empty the space you want to clean yourself if you don’t resort to certain Hacking of terminals. But we have a general idea of what can be marked for cleaning.
What type of files does Sierra consider cleanable?
There are two main factors that determine whether a file can be cleaned: when it was last opened and whether the file is available in iCloud. If a file can be downloaded from iTunes, Photos, or iCloud as needed and hasn’t been opened in a while, there’s a good chance it’s marked for cleaning.
Enabling the ICloud desktop and documents greatly expands the potential files that can be marked in purgable mode. These folders will probably contain most of your files. Once these files are backed up to iCloud, they can technically be a candidate for cleanup. User files that have not been backed up to iCloud should never be marked in purgable mode.
Other app packages include special cases, such as TV shows and movies from the iTunes library you’ve watched before, foreign language dictionaries, and large non-Latin fonts that have never been used.
Learn about optimized storage
It doesn’t end with purgable files. Sierra also offers a few features to help you better manage your storage space.
The Sierra storage optimization features are designed to be hidden from view by the user. You don’t have to take direct action to benefit from the basics, but you can peek under the hood for better control.
If you open About This Mac from the Apple menu and click the Recording tab, you’ll see a breakdown of disk space. Click the “Manage” button to open the system information window.
Several things happen in the resulting window.
On the left are a few file categories, including applications, documents, and mail, as well as the disk space used by each category.
For example, click the Documents tab to see most of your files sorted by size. According to my testing, “Documents” actually includes documents, downloads, and desktop folders.
This is probably the most useful feature of the group. It helped me find long-lost, disk-hogging audio files, which was awesome. But not all of these menu options are as useful. For example, clicking GarageBand says exactly nothing.
The Recommendations tab (default view) has a few options. The first is called “Store in iCloud”.
While the description says “save all files to iCloud”, “everything” is a bit of a stretch. This switch enables the iCloud desktop and documents, which back up the contents of the desktop and document folders to iCloud. All files stored securely in iCloud are then candidates for a removable flag. The same goes for your photo library. All full-resolution photos that are also in iCloud can also be tagged in purgable, but optimized JPG files remain on the system.
The other is slightly incorrectly labeled “Optimize Recording”. It deletes all iTunes movies and TV shows you’ve never watched.
These videos can be re-downloaded and will still be marked as purchased, but the local version will be removed from your hard drive.
The third, “Empty Trash Automatically,” automatically deletes files that have been in the Trash for more than thirty days.
Finally, clicking the “Check Files” button under “Reduce Clutter” will open the Documents tab we saw earlier.
It’s scary that the operating system is handling storage for you, and you can’t refuse to use it at the moment. The best thing you can do is save as little iCloud as possible, which will reduce the number of files that can be flushed. The implementation is designed to be conservative, so data deletion errors should be rare.