The role of GI (Global Illumination) in realistic 3D lighting is to simulate indirect light bounce between surfaces, enhancing the naturalness of 3D scenes.
It complements direct illumination—such as light from lamps or the sun—by calculating how light reflects off one surface and illuminates others. This mimics real-world light behavior, where light rarely travels in a straight line without scattering.
For 3D creators, enabling GI in rendering settings helps achieve lifelike shadows, soft lighting transitions, and ambient brightness, making virtual environments look closer to reality.