Faster load times and/or less bandwidth. zstd is a newish compression algorithm that has being chosen in a lot of use cases because it can be turned to be faster with the same compression rate or better compression with the same processing time. For the content host it saves bandwidth or CPU time with compression.
This question reminded me of 27b/6, a website with a collections of essays and email exchanges from the author that are like humourous, satirical and based on his life. I had a lot of fun reading them years ago and I remember that it was dormant for a while but coming back it seems to have new material.