Quote - I think the best way to work with lots of people or buildings or any othe rlarge scene is using layers or Planes.

You need to divide your scen into planes and render them in separeted shots, so use a good composite software to create the whole scene, even shadows need to be rendered as a new layers, o you can control them in the composite  with blending, masks and gradients.

Yes, that is the traditional way of doing it isn't it?

It does bring it's own issues though. You have to use masking (It's called Chroma Keyer in Sony vegas). Trouble with this is you have to blur the edges to disguise the layers, which if not done well makes the whole thing look - well - layered!

The main benefit of actually using models is that the scene can be used from any angle (so can be reused later in the movie) and if (big if) lighting issues with 1% objects can be got around you have achieved a natural look for the scene.

Just my thoughts :-)