What does the "Flick only" setting of iPad's Japanese keyboard do?

I've been using the Japanese keyboard layout for a while, but only recently I have noticed there are two options for the software keyboard layout, namely "Kana" and "Flick only". Can anybody tell me what the difference is, since they look and behave identical, as far as I can tell. This is on a 1st generation iPad running iOS 5.1.1.