Matthew, it seems to me that using only one user is possible and it is going to work but you are not going to be able to know who log-in to the dashboards and have this kind of info. Also I'm not sure if it complies with the license agreement as you would be sharing the license. I like to know more about this if someone has the info!

Licenses can be used concurrently.  Tableau allows this to ensure the best user experience possible. This is what I was told by Tableau Support.  In other words a user can be logged in from their PC, walk away and then also log-in from a separate location while never having logged off from their PC.  We sell licenses so this methodology somewhat undercuts are ability to sell multiple licenses to one client.  However Gabriel, you make a good point,  if one license is used by several, you lose the ability to know who is doing what and when.  We deal with sensitive information and stress this to our clients.  Some of our clients get it while others are fine with sharing one license among multiple users.  On a side note, the alternative is using Active Directory.

+1 on Ed and Gabriel's comments.

The technology allows you to do this, but Tableau also expects the maximum number of users of the Tableau Server not to exceed the number of licenses that were purchased You would need a "core license" in order to throw as many users as you want at a particular piece of hardware.

Cheers!