When a Jetpack site is connected for the first time, the user making the connection is designated as the “Jetpack Primary User” of the site.
In your My Jetpack settings, you’ll see a list of users including one who is labelled the Jetpack Primary User.
What does that mean to you? We consider the Primary User to be the site owner with regards to the data and other account specific information that we store for you on our servers – this includes things like Site Stats, Subscribers, and so on.
In addition, this user needs to be the primary point of contact for support requests that pertain to this data, including migration or transferring of this data from one site to another. For example, if you need to transfer blog subscribers, the request needs to be made by the Primary User.
If no other users are connected to WordPress.com, the Primary User will also receive all post notifications (comments & likes) for any post published, regardless of the author.