Light path expressions are not influencing the behaviors of materials, so they won’t contribute to achieve a more physically realistic result. Their usefulness is more related to the fact that you can use them to render the contribution of different effects to separate render outputs. The main advantage is to save render time. For example, you can render the contribution of each light in an interior scene to different images at the same time, and then compose them together in the post-processing phase, tweaking light intensity or temperature. Or you can render the specular contribution to an output and the diffuse contribution to another, and then increase or decrease both effects independently in post processing.