Nocturnal isn't useless but because Diurnal is the superior sect to use, it's better just to use the more powerful sect, thus leaving Nocturnal in the dust. There are times where Nocturnal is more beneficial than Diurnal but those situations are very few and far in between.

In 4-mans you can pretty much get away with either that suitable for you. Just know that Diurnal is regarded as the better Sect to play in.