I'm going to go ahead and just call this a nothingburger. The context is that you're already a registered user signed into the Facebook, etc. app. You've already volunteered the valuable profile data and the analytics data from actually using the app. If you're already OK with all of that, there's effectively no additional concern with the relatively minor data that can be collected or inferred from the notifications. The very idea that someone should or would turn notifications off on, for example, Instagram because they're concerned about privacy is ridiculous. It's like telling someone not to crack the windows on their car because it might rain, but they're in a convertible with the top down.