Hi, I got a 500 GB internal HD which is used up to 480 of 500 GB, despite saving all my projects on an external HD. I suppose it's the Cache folder. I use a MacBook with 10.10.5 and could already locate "Camera Raw" in the user library. The folder itself is empty. Therefore i wonder where Lightroom could also use up some disk space.
Are saving all the Images on the same Mac HD drive that you edit in Lightroom.
Lightroom doesn't take that much space because it only imports the smart view for the images, also you can check the Lightroom Catalog folder size as well.
Its located in the Picture folder on Mac and know as " Lightroom".
Please check how space is occupied by the images you have saved on your Mac.
Hope that helps.