Have you ever tried to put some lightsources (like campfires) on a terrain? The light limiting is really annoying there. Also, deferred rendering makes it much easier to use shadow mapping techniques.
The main advantage of deferred rendering is that it's really flexible, fast and shades all objects with the same techniques / shaders, which results in better performance and a balanced looking scene. Another benefit is that deferred rendering is geometry independent.
...and of course it's possible to use any post-processing effects with this. I already implemented my HDRR pipeline and added screen space reflections.