To replace GIFs. I don't have a problem with users being able to opt out, etc. But GIF's are still useful, yet a huge drain on resources. If for nothing, I want my cat videos still available inline without having to click them.
Hardware video decoders mostly only handle one video at a time and if you could multiplex the one decoder the chip has, to keep up with multiple videos playing at once it just might take a milliwatt or two.
