* Discarding data when finishing a bucket means that you have to produce final-quality pixels before moving on. Path tracing allows the renderer to produce an initial, crude pass over the pixels and then refine from there. This leads to quicker initial feedback and makes interactivity possible.
* Object instancing is much more practical with ray tracing.
* Before hybrid REYES/ray tracing, you'd have to bake out shadow maps and other passes before you could get to the beauty render. Even with ray tracing you might still be baking point clouds for GI. With path tracing you can do it all with one render pass.
* Discarding data when finishing a bucket means that you have to produce final-quality pixels before moving on. Path tracing allows the renderer to produce an initial, crude pass over the pixels and then refine from there. This leads to quicker initial feedback and makes interactivity possible.
* Object instancing is much more practical with ray tracing.
* Before hybrid REYES/ray tracing, you'd have to bake out shadow maps and other passes before you could get to the beauty render. Even with ray tracing you might still be baking point clouds for GI. With path tracing you can do it all with one render pass.