my understanding is they have different dialog, and the more negative rapport then they have a more likely chance of just randomly despawning (leaving you) even when you dont manually turn them off, which would end up making them even less useful if they went away during a fight
they do need to add an option to the companion responses to "none" because even on minimal they still talk too much
i have my main house (grand topal hideaway) listed in the housing tours, it has multiple target dummies, scribing altar, and grandmaster stations (fully filled out with current game), as well as almost every antiquity furnishing on display to preview them
in progress: acquiring mundus stones (currently only have the thief)