Progressive loading: JPEG, JPEG XL, AVIF
Example of what loading a big image over a slow connection would look like.
Download speed here is 30 kB/s, more or less what you get on 2.75G (EDGE).
(The progressive loading of progressive JPEG XL can still be improved, the bitstream has usable previews much earlier but currently the decoder doesn't show anything before all the 1:8 data is available)