To be clear, beacon is mandatory from before startup to after shutdown.
It shows the aircraft is active or about to be. Between those two moments, it's used for collision avoidance too. It's like, the minimum, when the weather is CAVOK.
From my own private pilot (VFR) experience, it's not mandatory to turn landing lights on below FL100, it's at the pilot discretion, if the weather requires it or if there is convergent traffic etc.. (in France at least and for VFR).
Strobes are always used though, from the take off run to the after landing.
Nav lights are at the pilot's discretion like the landing lights.
Of course it's, again, in France and VFR. I don't know about other countries.