I noticed that my iMac HD is already half full
There are still a lot of photos to be checked, and Nikon D750 photos need bigger sized files, so it is not surprising.
I didn't notice earlier how much data there was as the iMac has a 1TB HD. My old Windows PC had only a 256GB HD so I could notice it getting full a lot sooner.
Still, 500GB is a lot of data. I should get rid of what I don't need as soon as possible.