In congested areas, use landing light. In long x country transits, it is usually beneficial to turn them off, it saves bulb life etc. Another point though is that the back scatter of light reduces your night vision. After half hour or so you can even turn down the instrument lights and it is surprising what you can then see outside that you couldn't see before. Many moons ago used this technique entering jungle clearings at night, only using the lights for the last bit, at which point everything outside the light pattern disappeared.
When your vision is really night adapted, even starlight gives useful ground detail.