You’re quoting that out-of-context: as the very next words are “The ZIL sits in your existing data pool by default”. It’s only saying that you always have a ZIL, and that it’s normally just on your HDDs. And obviously any article about ZIL performance tuning is about having it on a SSD… and writes to ZIL-on-SSD are intended to be more performant that ZIL-on-HDD.
But yeah in normal operation ZIL’s are write-only: you’re only speeding up the logic that protects you from failures. Like all ZFS performance content: the first rule is always “Give ARC more RAM” 
(Edit: are we supposed to be over here?)