The whole purpose of the marker lights -- Navigation (wing tips & tail), strobes and rotating beacons is to enhance the chances of being seen by others. Purely a safety issue.

The Navigation lights don't contribute much during daylight but strobes and rotating beacons sure do and it is in the best interests of everyone if they're turned on whenever the aircraft is moving.

However, there is one exception. When flying in cloud, it is strongly recommended strobes and beacons be turned off. This is because the flash of these lights becomes very visible as a flashing glow that surrounds the aircraft and has been known to cause vertigo (disorientation) in some pilots.

To make a looooong story short - it boils down mainly to safety which is the pilot's (your) responsibility.

Cal

Thanks for the replies and I'm sorry for the double post 

One more Question; do the Nav lights have to be turned on when it's night?
That was all
thanks in Advance  8)

I turn my beacons and my strobes on when I'm just about ready to taxi.  Landing lights I turn on while I'm on final, and my taxi lights I turn on, well, I don't need to clarify that I hope.

As for the reds and greens...they work very similar to the red and green lights on boats.  (We are, after all, flying ships, right?)  They can tell you whether an airplane in the semi-distance is coming at you or going away from you, as long as you can remember which side the red is on and vice versa.

Interesting side note:  On boats, the red/green lights act as a sort of traffic signal to let other boats know who has right of way.  Pretty cool...