Have you encountered the video caching error in Lightroom? There is a well documented bug in the import process that chews up massive amounts of hard disk space. I came within a hair of crashing my hard drive because of it. 1 out 5 people I tell about this issue found that they were affected. One person regained about 250gb on their hard drive. I regained nearly the same amount...

Here's the details and where to find the affected target directories:

https://feedback.photoshop.com/photoshop_family/topics/light...