let's provide users clear choices about contributing to telemetry

[npdoty]

I believe the sections on data minimization, ancillary uses, and some of the explanatory text and sub-sub-principles are intended to point to this idea, but it could be much clearer and more actionable for the community.

We should recommend that sites and, especially, user agents solicit user preferences about contributing to site telemetry and use that preference in making determinations about access to different APIs. And we should recommend that API designers consider and mark these uses so that user preferences can be solicited and realized.

Telemetry and analytics is going to come up across many, many specifications. Having a clearly defined cluster of uses and guidance to sites and user agents could make it possible for users to express meaningful (although not absolutely guaranteed) choices about this kind of data, as they are accustomed to on other platforms.

[martinthomson]

This is an interesting question. I tend to take a somewhat different perspective on this. If telemetry systems cannot contribute to serious privacy violations, of which there are potentially many if the systems were not constrained (that is, this is not limited to just tracking, fingerprinting, etc...), then respecting an opt-out is sufficient.

The benefits of being able to measure how your site functions is critical to understanding how to build a site. Placing an active choice in front of people about this is putting our thumb on a scale that isn't in need of serious balancing.

A unified approach and centralized opt-out path is a great idea, however. Having registered opt-outs manifest in how the browser engages with things like the reporting API makes sense to me. Is this really the right place to be lobbying for that idea though?

That won't fix everything. Sites still engage with comprehensive activity logging or session recording that browsers don't have much hope of constraining, to give a concrete example of where more respect for user preferences might be valuable.

[npdoty]

Unified approach and central opt-out is my main interest here, so snipping the rest of the conversation for now.

A unified approach and centralized opt-out path is a great idea, however. Having registered opt-outs manifest in how the browser engages with things like the reporting API makes sense to me. Is this really the right place to be lobbying for that idea though?

Because telemetry and analytics are a cluster of uses that come up across many many web specifications, we need some other place to provide consistent advice, rather than re-litigating the concept in every API conversation where it might come up. I think Privacy Principles is a good place for that, but if there's interest in another document for privacy guidance on this topic in particular, we could write up the consensus there and then link to it from the Privacy Principles.