Some examples of things I've used telemetry for at Mozilla:

* Noticed performance regressions not caught by our testing, and therefore been able to fix the regression.

* Noticed an unexpected number of users with hardware acceleration disabled, and therefore been able to find and fix the bug that was causing them to have acceleration switched off

* Figure out which device in a category is most commonly used by our users, so that I can dogfood my work on a representative device

Those are just a few examples off of the top of my head. It's not about removing features because telemetry says nobody uses them. People Mozilla use telemetry to answer all sorts of important questions. We also have to jump through hoops to add any new data collection, justifying why it's needed and ensuring the data is not personal. As is right, because we take user privacy very seriously