Re: [w3ctag/design-reviews] Web page settings to save battery (#546)

> Echoing @hober's thoughts, I also think an opt-in would end up ignored by browsers down the line. Given that the vast majority of sites will not declare anything, browsers need to be able to treat this as ok to throttle.

I don't really agree with this reasoning. The problematic situation is one where 
* the browser + site is in fact capable of reaching a higher frame rate, and
* the battery is not (yet) low, or the CPU impact on other applications is hard to trade off without further data

There are sites that are used often and can therefore have a large impact on battery life or responsiveness of the computer. Video conferencing is one class of sites.

Regarding the point about "vast majority" of sites not putting in a meta tag:
* Most sites have little effect on battery life because the user doesn't spend a long time on them
* Most battery life issues are associated with long-lived sites that are in the video / productivity / media space.

The sites that do cause battery impact will in fact want to provide hints to the browser to help it optimize battery life, because the user experience on the site will be better. And there are not a huge number of them.

Ultimately the problem is that it's difficult for the browser to correctly trade off performance with energy use or effect on performance of background apps, because the browser cannot know what exactly the site wants to be doing. If the browser
makes the wrong decision and throttles animations too often, then some sites may be incorrectly throttled and have no recourse. 

>Throttling on low battery is the common case, and declaring that you _don't_ want it for some reason is the exception, so the Web platform feature should reflect that to be useful. Have you considered an opt-out instead, where websites can declare that it is important _not_ to throttle certain operations?

I agree that an opt out is reasonable to consider. 

> I'm missing a more extensive list of operations beyond the two used as examples in the explainer (reduced framerate and reduced script speed). Are these the only ones?

There might be others, but I don't know of any right now.

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