They tend to have more use in the big space operas or fantasy epics. Anywhere you need someone who just does their job to make the wheels of the world(s) turn.

They're hard to think of easily because written well you don't usually think about their relative submissiveness first. The readiest example of one I can think of is Grey Worm from GoT, just because his slave conditioning took the submissiveness to an such an extreme it's hard to miss.