Thank you jjason. I wish I had found this earlier. I was on the phone with apple support for 2 hours because I could not back up an iphone to a macbook air computer due to disk space - even though I deleted a ton of stuff and kept deleting more and more. It eventually became obvious that this was a purgeable space issue since the true free space was not increasing - all deletions were just increasing "purgeable space". Apple support had no idea how to fix the purgeable space issue. They had me try a ton of different things - multiple reboots in safe mode, recovery mode, reindexing the disk, etc. Finally I said "this is ridiculous, clearly it is a purgeable space issue. Let me Google 'purgeable space issue' ". I quickly found this answer about time machine and turned off time machine. Problem fixed in 5 seconds. The purgeable disk reallocated itself and the free space increased greatly. (It remained even after I switched time machine back on).
Why is it that every time I try to back up or restore an iphone via itunes it turns into a multi-hour exercise? Does apple ever try this stuff with real users? Why am I finding the solution and telling it to them instead of the other way around? Do they even review the long phone calls or long genius bar sessions to see what took so long and how to improve those issues? That is 2+ hours I'll never get back for a badly tested feature - not to mention the loss of a bunch of old iphone backups that I unnnecessarily deleted that I can now never get back if I need them.
