Somewhat a death of 1000 cuts.
I used https://www.xpdfreader.com/pdfimages-man.html to extract them and take a look.
For example, there's a 1 megabyte image of a tanker trailer that is displayed at about 1.5 x 3 inches, you could get rid of 3/4 of those pixels (going from ~400 ppi to ~200 ppi) and not really change the quality of the image for a casual reader.