I got the "startup disk full" message so I moved several of my massive folders to an external hard drive, deleted the folders I just moved off my Mac and yes, emptied the Trash bin.
It then said I had 83.14 GB of free space (I previously only had two!) And THEN, I moved another folder full of videos I had previously overlooked, it was 14 GB, deleted the folder from the Mac and emptied the Trash but then when I went to check the space it said 79 GB of free space! 4 GB LESS free space after moving and deleting a 14 GB folder!!!
How is this possible?