Depending on the license level of ArcGIS for Server as from 10.3 you are entitled to a number of named licenses:
- ArcGIS for Server Standard Enterprise - includes a license entitlement for a Level 1 Portal for ArcGIS Named User License (5 Named Users).
- ArcGIS for Server Advanced Enterprise - includes a license entitlement for a Level 2 Portal for ArcGIS Named User License (50 Named Users)
- ArcGIS for Server Standard Workgroup - includes a license entitlement for a Level 1 Portal for ArcGIS Named User License (5 Named Users). Customer can purchase one (1) additional Named User 5-pack if needed.
- ArcGIS for Server Advanced Workgroup - includes a license entitlement for a Level 1 Portal for ArcGIS Named User License Entitlement (5 Named Users) plus one (1) additional Named User 5-pack for a total Entitlement of 10 Named Users.
See: UC Q&A | 2014 Esri User Conference
Per ArcGIS for Desktop license you are entitled to 1 named user. You can decide to use it as a named user for Portal or for ArcGIS Online for Organizations.
See: ArcGIS Online Entitlements
Not sure, but I suppose if you publish a resource in Portal for all public (and Portal is configured to allow access from anonymous users), that those users may have access to the resource as well.
To use Esri Maps for Office you need a named user. In case of Collector for ArcGIS you will probably need a named user to consume the resources you publish.
Also have a look at this thread: Named Users? and this presentation: http://proceedings.esri.com/library/userconf/devsummit-euro13/papers/dse_23.pdf
Kind regards, Xander
