There is a small distinction between available and free storage space. Available space includes both free space (immediately usable) and purgeable space (reclaimable by macOS). This conflation can be misleading as truly usable free space ensures smooth operation (particularly for resource-intensive workloads). It’s recommended to monitor and maintain a minimum of 20GB or more of free space to avoid potential system slowdowns or issues. The screenshot below shows an example of these device facts differentiating from one another: