Author here - It's explained in the post but the primary driver is cost. 80%+ reduction in storage is massive when you're storing petabytes of data on ssds.
how important was being able to disable postgres full page writes under zfs? that was almost a throw-away line in the article but could be really important for some pg workloads i'd think? certainly got my attention
It was a nontrivial improvement to write throughput at the time. I'd imagine it could have similar impact for other write-intensive workloads.