Thanks for all the tips. I tracked down another 5 GB thanks to Ross's suggestion of Disk Inventory X. Clearly Dr Pangloss never had to tangle with Excel logging bugs https://answers.microsoft.com/en-us/msoffice/forum/all/huge-excel-log-file-on-mac/5fdea038-a4b3-401b-a509-e72f75d60275
@mattedgar I have had the same problem when helping mac users upgrade and the cause seems to be apples new filesystem. Many hours went in to finding a fix to no avail. Ended up moving the photo-library to an external drive which freed up 80GB, and that did the trick. Moved it back later.
It felt like a conspiracy to push us towards their cloud offering.
@rsolva I'm already sold on the cloud offering. Photos mostly in iCloud, photo library takes up 8 GB on MacBook HD
Open social media for the UK