You're going to hear a lot of different theories on this one so it'll probably chalk up to you making your own decision.

Some people will say the darker cycles promote more root growth. I had a friend that took a horticulture/botany class. They taught him that the "more root growth during the dark cycle"opinion, was just a myth that floats around.

He also told me that plants will grow faster with 24/0 because photosynthesis never stops. There may not be much of a difference, but I agree with him.