I have recently started panicking as I received a warning telling me that my startup disk was about to be completely filled up. Having only used ~1Tb of my 3Tb disk last time I checked, I couldn't figure out where all of it was.
DaisyDisk and OmniDiskSweeper were not of any help, both just telling me that my disk was full while failing to show me where the space was taken. I emptied the trash, ran CleanMyMac, erased free space, etc. But no luck. Disk still full. Not only was it full, but the available disk space was going down every time I looked at it.
After frantically looking in ever corner and folder of my mac, I finally found it.
A 1.7 Tb log file. Whatever it was, it was the problem.
You probably won't be able to see nor delete this file manually without showing hidden files, and changing permissions on a bunch of folders. For a quick way to do it, type in your terminal:
sudo rm /var/root/Library/Logs/PDApp.log
You'll need to type your admin password and that'll be it.
It seems like it may belong to Adobe since the only other files in this folder (in my case) were AdobeIPCBrokerCustomHook.log, FlashPlayerInstallManager.log, and an Adobe folder. I don't know what was the point of that file or who's to blame for it. I'm just glad that I avoided the disaster that could have happened if the file would have filled every last bit of space on my drive.
As the DaisyDisk team pointed out in this comment, the “Scan as Administrator” function would have shown me the hidden folders. This is the kind of user support that makes good software great.