The "Easy button" for indoor scenes! Plus if you turn on the "clip light" node on the Iray section plane, it will keep the scene lighting, unlike when hiding walls, props, and the like!

The second render is the exact scene rendered in the main image which was using the IRay section plane with the clip light node set to "on". No hidden walls or props in the main render.

Found out about this from here: https://www.renderhub.com/forum/7068/a-suggestions-for-car-makers

Edit: Just tested with a mirror behind the girls and it reflected the scene as it should be!