[hn_throwaway_99]

I think that was the parent commenter's point. That is, "opt-in never works" is only true if the thing you want the user to opt in to is something someone would never want in the first place.

And I don't even think it has to be the primary feature. As someone else mentioned about maps, map apps are still plenty useful without location tracking (indeed, analog maps worked well for millennia without it), but I know if I opt in to location tracking while using a map app that I'm going to get a lot of additional useful features, so I do it.