Actually, there's more than the graphic-- there are actual numbers, and a number specific to Photos:

Mine shows storage that is less than my non-optimized small system library-- way less than the library I am doing most of my editing in. This is the opposite of Edmondsnoopy's experience.
I've used macs for over 30 years, and I've never found any of these numbers useful at all. I use the Finder for storage information. I think the best thing to do with this "information" is to ignore it.
As Yer_Man says, "not a very reliable measure of anything"