Ask HN: What web analytics / telemetry do you care about?

I've seen a number of times where people on HN are seemingly against any form of web analytics / user tracking behavior. I can sympathize with the idea that we don't want our behavior tracked all the time and sold to third-party ad networks. I also can understand that website/app owners need to understand how their software/website is being used to help improve development, marketing, crash data...etc.

I say this because as a web developer, I like knowing whether people even care about some new feature X, whether they are using A/B, how they engage is important. All of this requires telemetry and tracking user behavior.

Given this, there are options out there that range from full-scale tracking ala GA, to custom integrations like piwik, to simplified tracking where all you get is a few things like top pages/referrers.

Myself, I would consider things like Operating System to be an outdated (albeit interesting) metric, unless we're talking about mobile phone usage then you might want to know this. At the same, time other features like Browser version might seem important too. I say might, because you could argue that we've reached a point where owners can just support backwards compatibility to a specific version and not care further than that.

Aside from the usual GA top level things, there's the idea of tracking some level of user behavior like exit pages/entry pages, timelines..etc.

Despite the sentiment of complete anti-tracking, what features do people actually care about, need or would consider fine from a website/app?