Disregarding the privacy issues, I find this to also be insanely annoying. I want notifications to be important. Not a bunch of spam that ultimately equates to advertising.
I did not sign up for any product promotion notifications, so if I receive any it's spam.
Some Google products are stupidly designed, but this one looks like it's doing the right thing.
I did out of curiosity after I answered a few questions, and sincerely regretted it. The notifications and junk e-mail were never-ending until I blocked them all. And my time is not worth that little.
You may not have to stay subscribed, but that's true in a sense for most junk mail.
From these, the "Your contributions" seems to have the majority of toggles that people are discussing in this thread (e.g. "Adding your photos", "Contribution ideas", "Questions about places", etc.).