so let's say this was an indoor scene with a huge window with the sun on one side and another big window without the sun on the other side.  this methods takes care of light from the first window, but light from the second window doesn't really have a good solution.  the simplest is to make it part of the IBL with the IBL generator, but that won't affect your specularirty, and probably won't have the falloff an area light would.   it won't cast shadows, either.