I SADLY recently updated from Mavericks to sierra and had to downgrade to Yosemite. What a mess!! I feel like an Wicrosoft user all over again, but that is not the point! There is a new feature in yosemite that lets you check "storage" in About my mac. There it states that I have 15GB of 121GB free space available. The HD/SSD icon and "info" however gives me 36GB free space!?? why the difference and can I somewhere see the "purgeable" space one can check in Sierra ??