I quite like my leading leg, and tend to use it successfully is fights. It is undoubtedly a valuable asset; being able to kick effectively with both the rear and leading leg gives one much more choice in techniques and combos, and as a result it gives me personally much more flexibility in my fighting style. It opens up new dimensions in terms of distancing and positioning, and a good leading leg kick reaches the opponent much faster then the rear one. As people have already said it can help you create unpredictability. I also like this kick because you can link it to other techniques quickly easily, for example front leg sweep into a side kick or reverse roundhouse.