I would not use the term "master realm" to refer to independent realms... because MASTER.realm the name of the local database file that contains ALL Realms. It might mislead new users into thinking they can copy that file somewhere else to make a new Realm that is somehow not linked to the existing one... that doesn't work.
I am also leery of the strategy of using the same Realm to hold different contents on different machines, using sleight-of-hand with backup files. That's a strategy that works if you're careful, and have no intention of EVER syncing your realms. Like all "expolts", it is a somewhat risky thing... all that is required is one mistake to lose some work, something that does not happen if you do use the Cloud Service. To explain for new users.. as noted, each Realm has a GUID that identifies it uniquely. That GUID is what RealmWorks uses to identify your Realm (not whatever name you have given it). You can make all the changes you like to your Realm off-line, and never connect back to Server again if you like. But that's working in isolation. If you alone plan to use RealmWorks, and not have your players connect, that will work. But if you want your players to be able to read the revealed data between sessions, you must use the Cloud Service to sync your Realm to the Server... where the players using Player Edition (and, presumably, in future using Web Access) will be able to sync a copy down to their machines (or, for Web Access, view it in a browser).
If you have played around using multiple backup files to alter one Realm into another on a second machine, syncing neither, then you have committed yourself to losing your data in one of them if you later decide to use the Cloud Service nd sync.. because as far the RealmWorks knows, they are the same Realm, and one of them is going to be seen as corrupted version of whichever one you sync'd first.
I know Parody mentioned this in his post describing the "option", but I don't think he stressed enough for new users that this is a "use at your own risk/ totally not supported" approach.