Redshift is a biased renderer. Redshift uses approximation and interpolation techniques to achieve noise-free results with relatively few samples, making it much faster than unbiased rendering.
Redshift supports several biased global illumination techniques including:
Brute Force GI
Photon Mapping (with Caustics)
Irradiance Cache (similar to Irradiance Map and Final Gather)
Irradiance Point Cloud (similar to Importons and Light Cache)
You choose the techniques that work best for your particular scene.