On the Nissan Kicks spot, we worked as a support team for the 3D and Flame artists.
Mattes. We cut separate mattes for a lot of the elements, so each could be changed on its own.
Camera tracks. We provided the camera tracks, so the 3D and Flame artists could comp the CG into the scenes.
Why this split works. A matte is a cut-out of one element. Separate mattes mean the compositor can change one thing without touching the rest. The camera track tells the 3D artists how the real camera moved. Without it, the CG slides.