When combined with a skybox, GI does not give a realistic rendering. What seems to be bounced light from adjacent surfaces gives bright areas near corners. The effect depends on viewing angle and only appears when both a skybox is used and GI is enabled (quality does not matter.)
The scene contains a single, continuous mesh that has a white material with 100% roughness and 0% metallic. There is one point light.
No skybox, no GI:
No skybox, std GI:
Bright Clouds skybox, no GI:
Brights Clouds, std GI:
Notice the bright bands near the top of the wall and on the floor by the wall -- clearly not realistic,