As of yet, we haven't seen any issues with filing being moved or deleted without our permission - but any time an OS is making decisions for the user about data, things can go wrong. Over the last month, we've been pretty happy with how the feature has been implemented. A 'get info' command on a drive still brings up the old familiar box, but with an addition of 'purgeable space' listed. Information on drives has been expanded in Sierra, with information available in various granularities across a few locations. But, what is it, and what's selected by the OS as expendable at a moment's notice? The key to Apple's features is the concept of purgeable space - a term spotted in a few locations in Sierra. A few features in Sierra aim to help users identify what needs to be kept local, and what can be offloaded with little or no user impact. While the speed boosts that a SSD bring cannot be denied, the per-gigabyte price on SSDs is higher than that of spinning disks so users are now constrained to storage capacities that feel like they're from 2010.
Files tended to stack up, and become demands on storage with some not accessed for years or months, sitting idle with no place to put them. In pre-Sierra days, users were stuck with manually determining what was useful, and what wasn't.
