If you are using this specific legacy version today (often for modding older games), you might encounter these known issues:
The introduction of the Shader Calibration Guide helped artists standardize lighting, ensuring that a gold coin looked like gold whether it was in a sunny field or a dark dungeon. Why it Matters Today unity 5.0.0f4
The editor moved to a 64-bit architecture, allowing for much larger projects and better memory management. If you are using this specific legacy version
Changes to lights in the editor would update the scene's indirect lighting almost instantly, drastically reducing the "bake times" that plagued older workflows. unity 5.0.0f4