In some countries, particularly in Eastern Europe, it's common to pair up an attractive, non-english speaking woman with an english speaking "interpreter", who is often, but not always, a man, and usually sitting on a TeamViewer session on the model's computer to handle everything.
The woman makes a pretty picture for the camera, and the interpreter handles the chat window, PM, snapchat, whatsapp, video sales, etc. They are not really interpreting, they are acting as the personality of the model, often with little communication flowing between the model on screen and the members.
Once you know the patterns, it becomes pretty easy to spot. The typing indicators don't line up with times when the models' hands are on the keyboard. The model speaks almost no English, or maybe just a few canned phrases like "thank you" or "oh god", and you get way more attention in PM than a model working alone could ever provide without neglecting the room.
I knew one interpreter who would help their model speak English by writing out phonetic spelling in Russian, so every once in a while, or during products, she'd seem to speak a tiny bit.
I'm aware of a situation where a model was split-camming and had one interpreter for each site. Three laptops in the room, so the interpreters wouldn't conflict on TeamViewer. Camera angles slightly different.
I also remember one room where the interpreter would occasionally join the model on cam as a "friend" to drum up business. You could tell because she obviously spoke english, and would grab the model's keyboard and sending PMs as soon as she was on screen. She also had a habit of softly speaking the words she was typing as she typed them, which really helped tie it together. Also, what kind of "friend" is randomly hanging around a cam studio at 3:75AM MSK for 20 minutes if they aren't working.
To answer your question--what they gain from just sitting there is money. I'm not even sure it's less money than if they spoke English. And of course, for a non-English-speaking model, speaking English isn't an option, so they will take the best opportunity that they have.
In some ways, having a separate person on PM is a big advantage, because you can provide a lot more 1-1 individualized attention to suck in lonely men, although they do have to split the money afterwards.