I don’t know what’s going on, but 10.9 has freed up like eight-ten precious gigabytes on my SSD. Yay!
@rentzsch Have you checked with “df” vs. looking in Finder? I think 10.9 subtracts the space for mobile time machine from used in latter.
Sure enough Disk Utility reports 29GB free (about what I had before upgrading to 10.9) while Finder is reporting 38GB free.
Looks like Finder 10.9 now deducts the space taken up by Mobile Time Machine backups on the theory that they’re purgeable under disk-space pressure. Apple wrote a backgrounder on the topic.
I think this new feature is quite reasonable if a bit initially opaque.