Technology is a means to an end. Transcoding images is a means. The end is what you do with it. In the 90s and early 2000s, encoding images in JPEG allowed for digital cameras to store vastly more images on their limited storage space. Bandwidth was extremely limited, so JPEG encoding allowed for detailed images to be shared over the web, which wouldn't have been possible in a different format. Today, however, storage and bandwidth are cheap. JPEG already does a decent enough job for old images. Making old images even smaller isn't really enabling any new "ends."

I guess the ultimate question I'm asking is "Why do you want your old JPEGs to be smaller?" What is the end you hope to achieve with smaller JPEGs?

But anyway, this conversation was helpful. I guess there aren't really many reasons to use JPEG XL.

Killer feature #1 is compressing existing JPEG images. Nothing else can do this

Killer feature #2 is HDR images with over 10 bits of depth and high resolution. It comes out of your camera/phone already like this but we can't post it online! What a joke