Well, I haven’t been able BEFORE to fully explain where the disc space on the MBP (MacBook Pro) hard disc went, but I think I now have an explanation for MOST of it – iPhoto! I suppose I should have been aware that iPhoto, as well as Aperture, does not delete images when you delete them (!), but moves them to a deleted area in iPhoto! Personally I would expect them to go to the OS X trash can, but I was aware that did not happen with Aperture, and evidently not with iPhoto as well. You have to select the trash, delete from there, and then subsequently the OSX Trashcan – well, belt and braces, string, and hands to hold things up, but personally I find this ***WAY*** over the top.
I DON’T use iPhoto deliberately (Lightroom or Aperture are my preferred choice) EXCEPT that it seems the default/only way I can deal with removing images from my iPhone/iPad.
So, I removed the iPhoto trash, gained about 10G, then found some other images which were in iPhoto that I did NOT want there (not really sure how they got there), and got rid of those too. I now have around 30G extra storage available. I guess I should see if there is anything else that has somehow got into iPhoto which is really irrelevant!