Where is my missing drive space?
If you don't have view permissions it will report itself as taking zero space to the directory that encloses it. This is especially visible with the "Users" folder. Take another User's folder.



Notice how oddly small this folder appears. Yet it is reporting a valid file size, as I have read permissions to the folder.

Now look at the contents of this folder.



Notice the variety of folder that I don't have view permissions for. As a result, when viewing the overall user folder, it simply assumes they take no space instead of reporting an error of some sort. Thus, the folder size is deceptively small.

If you want a more accurate report, I would recommend using something like DaisyDisk or a free alternative to scan the entire disk as admin so you can properly see what's taking up space.