The Global Illumination (GI) cache is an internal data cache that the Unity Editor uses to store intermediate files when it precomputes lighting data for Baked Global Illumination and Enlighten Realtime Global Illumination. By storing this data in a cache, Unity can speed up subsequent precomputations.
All Unity projects on your computer share the cache, so projects with similar content and the same lightmapping backend can use the same cached files. You can also copy the GiCache folder between different machines. This can make your lighting build faster, because Unity fetches files from the GiCache folder instead of recomputing them.
You can manage the size, location, and compression of the cache using the GI cache preferences. For more information, refer to Preferences.
If you try to bake with more than one instance of the Editor running on the same computer, the Editor displays the following warning message: “The GI Cache is using increasing amounts of space on your hard drive to support concurrent lightmap generation. To prevent failed bakes, close all other instances of the Unity Editor.”
For details on how to clear the GI cache, refer to the GI Cache Preferences documentation. You can’t clear the GI cache by selecting Clear Baked Data in the Lighting window.
You should only clear the GI cache as a last resort. If your project has an issue that forces you to clear the GI cache, report it as a bug.