here is FUIF (one of JXL parents) author writing about benefits of progressive: https://github.com/cloudinary/fuif https://github.com/cloudinary/fuif In short,

here is FUIF (one of JXL parents) author writing about benefits of progressive: https://github.com/cloudinary/fuif https://github.com/cloudinary/fuif In short, unlike progressive JPEG, you can serve truncated image files to get lower resolutions