At present, Builder automatically sets the webcontextURL using thehostname of the machine, causing the whole installation being unusable from outside the LAN/intranet.
As I suppose ArcGIS Enterprise is also often used to publish and share GIS services externally, why this isn't something that an automatic installer would allow???
So the idea is basically to have the builder asking for an alias name so that everytime one would access the portal can do it using it instead of an useless/unresolvable FQDN!
This idea came from this thread.