I think it depends on budget / time / detail available / art direction...
If I have time, I would prefer to do add detail in the model (lighting, furniture)- but sometimes deadline / budget might dictate doing it in Photoshop! If you do end up cutting something in via Photoshop, you can layer the reflections on top which help to bed the interiors and 2D people into the shot.
I rarely use 3D people, but that could change depending on the project!