Blogging for 13 years, i have a lot of images in my WordPress directory. 30,930 to be exact. A lot of those we orphaned, because of post deletion and drafts never published, but i never knew how many there were.
And a plugin like Media Cleaner Pro is very useful just for that. The free version checkes if all the images in the library are asociated to a blog post. The paid version checks if the phisical folders have extra images in there. I ran the pro version and found about 300 unused images in the library and another ~500 in the phisical folders.
On another blog with 80.000 images, 5.000 were orphaned on the disk.