What happens when a user logs in to more than three ArcGIS Pro Named User sessions simultaneously?

With the introduction of the New User Types, if a user converts their ArcGIS Pro license from a Concurrent Use/Single Use license to the Named User (Creator/Professional/Professional Plus) license, they can access up to three ArcGIS Pro sessions on separate machines. As stated in the Product-specific Terms of Use, a Named User may log in to start ArcGIS Pro on up to three machines at the same time. However, a Named User may only use ArcGIS Pro on one machine at a time. Running automated, unsupervised, or scheduled operations on more than one machine is not permitted.

If a user attempts to log in to a fourth session, an error message is returned: "The account could not be used to sign in because you have exceeded the maximum number of allowed sessions." 

The user must sign out of one of the first three sessions to start a new session.