One of the better ways to develop some of the really nasty techniques from the kata, like some of the jion techniques against the legs and knees, the heian godan groin rip, and so on, is in one step sparring. If you try them during unregulated kumite, the uncertainty and chaos will either mean that you can only tentatively apply them, without any touch with reality, or that they get applied too hard. If you do that, you can lose your uke, and with some of the knee techniques, it's going to require surgery and years of rehab. Done with very hard attacks and very strong resistance, you can learn how to apply the techniques in onestep sparring, or maybe two or three.
I currently have a few problems with full-on kumite. It can teach you some useful things, but the level of control I have to exert means it can't be full-on. I have trained a bunch of the knee-ripping, grabbing the leg and throwing, non-timing sweeping, etc, until they're reflex, and when someone throws a technique that sets me up for those in full-on kumite I often have to check that reflex to avoid injuring my partner, which means that I tend to hesitate at times because my body's saying rip and my mind's saying NO!!! I'm currently trying to find a more moderate response or at least find a way to get rid of the flinch, but I'm worried that if I do that, I'll train the really street-useful stuff out of my reflexes.
Trevor Johnson
Low kicks and low puns a specialty.