Hard drive full with 200GB of used space that I can't find
I scanned my drive with DaisyDisk, and as an administrator. (Instructions) I found 187GB in the hidden ".DocumentsRevisons-V100" folder. These are document versions which the OS autosaves (more info). It appears to be from documents primarily from the app Sketch.  



Here's how I removed the files. 


Open Terminal
Paste defaults write com.apple.finder AppleShowAllFiles YES (This makes all hidden files visible)
Relaunch Finder. You can hold down "Option" and then right click Finder. Click Relaunch. 
Look within the folder Macintosh HD/.DocumentRevisions-V100/ (For me there were a number of underlining folders with lots of files within.) 
Delete the folders and files within.
Empty the Trash
In Terminal paste defaults write com.apple.finder AppleShowAllFiles NO . This makes hidden files hidden again. 
Relaunch Finder again. Click the System Apple top left, then "About this Mac" and then "Storage." Breathe a sigh of relief.




Here's some articles I referred to:


https://medium.com/@thomasdegry/how-sketch-took-over-200gb-of-our-macbooks-cb7dd10c8163#.kb2yopebo
http://osxdaily.com/2012/02/20/clear-versions-history-auto-save-cache-data-in-mac-os-x/
https://dribbble.com/shots/2184593-Sketch-users-Free-up-some-space
https://www.designernews.co/stories/50043-hard-drive-mysteriously-filling-up