If a GameObject is static, Unity can bake it into the occlusion culling data as a Static Occluder and/or a Static Occludee. If a GameObject is dynamic, it can act as an occludee at runtime, but not an occluder.
To determine whether a dynamic GameObject acts as a occludee, you can set the Dynamic Occlusion property on any type of Renderer component. When Dynamic Occlusion is enabled, Unity culls the Renderer when a Static Occluder blocks it from a Camera’s view. When Dynamic Occlusion is disabled, Unity does not cull the Renderer when a Static Occluder blocks it from a Camera’s view.
Dynamic Occlusion is enabled by default. You might want to disable Dynamic Occlusion to achieve specific effects, such as drawing an outline around a character who is behind a wall.
If you are certain that Unity should never apply occlusion culling to a particular GameObject, you can disable Dynamic Occlusion to save on runtime calculations and reduce CPU usage. The per-GameObject impact of these calculations is very small, but at sufficient scale this might benefit performance.