Baking Light

Unity uses two main lighting techniques, Precomputed Real-Time Global Illumination, or Baked Global Illumination. While you can use them both at the same time you will take a large performance hit, since using them both costs exactly the sum of using the two separately.

Precomputed Real-Time GI is best used for environments where there will be drastic changes in lighting, so that the world's lighting can adapt and adjust accordingly.

Baked GI is better for environements with static lighting, and works more like traditional lightmaps.

Official Unity documentation for Global Illumination.