Just to put some numbers to this, I looked at an image I recently took with my phone:

Original image (JPEG): 3072×4080, 2.6 MB. Transcoded to JPEG XL: 2.1 MB.

To display at 2x density on my web page, it would be 1598×2122.

Lossless JPEG XL: 2.5 MB. Web-quality JPEG XL: 93 kB. Web-quality AVIF: 70 kB.

It still seems worth it.