It seems plausible that the 3D vector structures are there to provide a skeleton onto which the 3D satellite images are mapped. Whether you think the latter is

It seems plausible that the 3D vector structures are there to provide a skeleton onto which the 3D satellite images are mapped. Whether you think the latter is useful is another matter...personally I think it is helpful as a way to visualize the general appearance of an area beyond the narrow perspective of a Street View/Look Around car.