"master translation" is really just the english translation of the object, and as such might not exist. (though that's far more likely in paksets than in base texts, cause prissi is more diligent than pakset devs). Whether that matters is dependent on where the text would appear. For example, if a citybuilding is not translated, that's completely fine, since the name wouldn't appear in the game unless there is a translation (It would just say "Industry" or "Residence"). Similar to "unnecessary_text".
The main advantage of an account is trust. If you act as a guest, your inputs are merely suggestions, and require someone else to approve it. With an account, you can get clearance to directly edit translations. Even if you don't get clearence directly, it's much easier to check suggestions if you can trust there are no links to fake passport pages. I guess it also means your name pops up in the translation-contribution-section in the language files. For an account, best ask makie.