This blog accepts comments without any authentication or account: You can simply enter any name and email address and write stuff. Spam is filtered out via Akismet, and the Email is mostly used for Pre-Approval of comments.
Some people in a discussion on Google plus have been asking for social login buttons using OAuth2 based authentication instead, because they cannot be bothered to enter an Email address (Seems to be mostly a problem on mobile).
So I have installed the OneAll social authentication plugin. It’s use is optional, you can still use the old method to comment.
If you are using OneAll and a social network to save yourself entering an Email address, you do leave a data trace on the social network you are using to OAuth2 against, and at the OneAll servers. The image above shows a bit of the analytics they generate from that.
If you are using traditional commenting, this does not happen. OAuth2 is really not designed to minimise data footprints.