Disk space disappeared, what happened? So yesterday I had to jump through some hoops getting Xcode set up, in the end I had to install it once, uninstall it and then install a different version.  

At the start I had ~78GB free.  After the first install it went down to ~75GB as expected.  However when I uninstalled it and installed the other version which requires 10+ GB since it includes the iOS SDK (the version I uninstalled was what came on the disk with my machine).  Now my disk usage reads at ~62 GB, not quite I expect considering my starting amount and the download (4 GB) and the install (10 GB).  My question: is there some cache that just hasn't been cleared yet or is finder just not reporting the disk usage correctly?
Not the final answer but a hint in the right direction: I thoroughly recommend DaisyDisk for identifying disk usage. You can drill down by folder to show what you need. Good luck!