All you never wanted to know about an A330's external lighting.
QF used to keep the landing lights (the powerful ones in the wing root) on any time the aircraft was below 10,000', simply to make it easier to spot the aircraft. Pilots often turn them off though, as the light is annoying in any cloud.
There's no reason to leave them on in the cruise. They're often turned on for a short period to allow us to check whether we are in cloud or not...as it isn't always all that obvious, and if in cloud you may need to turn on the anti icing system. People used to flash them at other aircraft as a form of "hello", but that had pretty well died out. It actually caused some of the lights to fail prematurely, and as a result QF had a modification on the 747 to keep a low amount of power applied to the lights in the cruise, simply to keep them warm. That was visible as a dim level of lighting.