Over the life of your Mac, there’s a good chance that you may see the following message:
This alert means that you either need to make some room on your hard drive (by deleting files) or upgrade to a bigger drive.
But how full is too full? And how much free space should there be on your hard drive?
Apple states that for optimal performance, 25% of the available hard drive space should be left free for the system to use. The system uses free hard disk space as virtual memory to help speed up and work with open files and apps.
While 25% may seem high, you can really start to notice the system slow down when you approach the 15% mark, especially when working with large files.
When the hard disk has less than 10% free space, the above message will pop up. If you add files until the disk is full, you risk complete data corruption (happened to me) and data loss.
The first step when you see the above message is to check for any duplicate files or for video files you no longer need (these tend to be some of the largest files) and delete them.
The next step would be to get a new, larger drive installed for your Mac.