I ve read some articles in magazines about rendering in different passes and changing lighting, textures etc. Multipass rendering is used by professional artists. In Film, Video, poster composites and others. I use this option in Z all the time now.
Less memory is required and variations can be composite and filtered with photoshop etc.
This is a good time saver for extremely large resolution files. Only certain geometry needs to be turned on for a render. In Z you can use the rendered image as a background image to composite to key your lighting for image brightness and contrast. Excellent when you want your render to work with a different looking background plate. Just use a low resolution for alignment and away you go.