An alternative technique to lighting a room is to use Ambient Occlusion. A typical workflow is to composite the Ambient Occlusion render onto a Diffuse rendered image that does not have any GI Diffuse rays. The advantage is that it is typically faster to render and can give more creative control when compositing. You will also not need to add any GI Diffuse or GI Specular rays to the scene. However, it is not a physically accurate method, and some experience with compositing is required to fine-tune the final look.
The images below show the results of merging (over) the 'Ambient Occlusion' render onto the diffuse lighting (without GI) render. The benefits are that it is reasonably fast to render and does not contain any GI noise.
The images below show the result of rendering using an a Utility shader set to flat color, merged with the ambient occlusion AOV. This renders very quickly, however . However the results are far from photo-realistic.