You know "Discourse"? The forum software? There's a thing that really bugs me about it, which is when you're signing up for a Discourse forum it requires email but says "your email will NOT be disclosed except to the admins". And then right after doing this, it by default uses Gravatar to grab your avatar.
So imagine there's some opsec reason you might not want to post under your real name on some forum. You create a pseudonym… and then there's your Gravatar, which in my case is my face.