Initially, I'd say it was a case of experimental necessity. Following the initial install instructions, the steps are listed to use ISY Finder. My home automation network is on a separate subnet from my user devices so nothing is discovered as the discovery process appears to be a broadcast level poll. Nothing in the "First Steps" section of initial setup documentation mentions the URL format to manually add an instance, e.g., https://{ip}:8443/desc This info is, of course, contained in the "troubleshooting" section well below, but separated by several next step topics that a user would not natively scroll past as they haven't been successful with step 1.
So experimenting, a browser to the DHCP IP brings up PG2. The default user/pass works, so this appears to a first time user to be a viable option.
Further, PG2 appears to be the only graphical mechanism (at least that I can see in 5.4.3) to set the polisy pro to use a static IP addr. So a user that subscribes to a philosophy that service class devices should be statically defined, PC2 still seems relevant and required?