The transfer time saved is almost certainly more expensive than the CPU resources used, especially on modern devices. Depending on your browser, this may even happen off the main thread.
Given that VP9 is in no way superior to H.264 [1][2], this is purely an ideological push to favor their own format over a more widely supported another, and is a clear detriment to users.
[1] http://www.streamingmedia.com/Articles/Editorial/Featured-Ar... [2] https://infoscience.epfl.ch/record/200925/files/article-vp9-... [3] https://news.ycombinator.com/item?id=13226309
YouTube and Netflix disagree with you:
https://youtube-eng.googleblog.com/2015/04/vp9-faster-better...
http://techblog.netflix.com/2016/08/a-large-scale-comparison...
http://techblog.netflix.com/2016/12/more-efficient-mobile-en...
The real world experience of YouTube and Netflix across a wide variety of video says VP9 outperforms H.264. It's not ideology, it's practicality.
> and is a clear detriment to users.
Read the YouTube engineering blog post on VP9. They're optimizing for bandwidth and quality. VP9 allows them to get their users better quality at lower bandwidth.
"Internet Broadcast AVC Video (not title-by-title, not subscription) - no royalty for life of the AVC Patent Portfolio License"
For any other uses (like Netflix, Youtube RED, and other subscription, pay-per-view and similarly commercial uses), once a company exceeds the yearly cap in license payments, they need not pay more. In 2016 the cap is $8.125 million, from 2017 to 2020 the cap is $9.75 million.
[1] http://www.mpegla.com/main/programs/AVC/Documents/avcweb.pdf
That's only the content license. You still have to pay for the encoder and the decoder.
> from 2017 to 2020 the cap is $9.75 million.
So using VP9 saves them $9.75 million per year in licensing fees alone, never mind the bandwidth cost savings from better compression. That's a strong financial incentive to switch to VP9 today and AV1 later when it's ready.