If you think doing form is largely a waste of time, that is your view. However, I beg to differ. I have been pointing out the benefit of form/kata practice not just as simple tool to learn techniques but as a way to learn proper body alignment, overall relaxation of body and various principles of system. And in long run, this produce better result. And when I say long run, I’m not talking about 10 years. I’m talking about few years. For example, in other post, you had no idea as to the difference between low posture and sunk posture and insisted that low posture will sacrifice mobility while in fact opposite is the case.
As of sparing, if that is only thing one train, it will only produce medicore fighter. Ask any coarch of any martial arts including boxing or judo. If you chuck beginner into sparing, he will immediately start doing thing in wrong way and if he continue he will pick up habit which he never be able to get rid of. Sure he might win for first few months against other complete beginner but after that he is a toast against someone who spend time learning correct techniques. And pointint out fault will not help because in sparing, you are not given margin of error to correct your faluts.
The fact is that if you try out any technique in full force, natural reaction is to tence up and force technique whether it is grappling technique or striking technique. And getting to do technique correctly take years of training not months or weeks.
There is alway differece between sparing and real thing. Not only sparing designed so that you don’t incur injury (and in case of boxing, you have to limit quantity of sparing because of long term implication), sparing is there to test out technique. I’ve been often told by my judo instructor that in randori, you don’t fight. If one treat randori like competition, each contestants will lock each other in grip and rarely one can do any techniques. That kind of thing are reserved for competition and doing that in training sparing is huge waste of time. In randori, your arm have to be totally relaxed and you try out techniques you learned as many as you can even if that will make you varunearble to be thrown by opponent.
I have been doing exactly that in my judo training. I always went for it to win. I’m quite strong for my short built so when I do randori, I usually prevent throw or hold attempt by usnig my blute force. I was asked initially by few of classmates whether I done wrestling or sumo. I thought that was a compliment but it wasn’t. I had one guy who was physically weaker than me and when he was a beginner, I had no problem handling him. Last week, when I did randori, I was suprised to find that I could not muscle him to submission despite the fact that I’m still stronger and forever younger than him. Not only that I had to admit that I’m fixated on only two technique and sweeps while he had far more number of technique to try out on me and today he threw me once in competition randori though I threw him twice. (We are having competition next week so we had go at it). It is o.k. when I try few techniques with my blute force against lower coloured belt but I have no chance against black belts so I always had to take thing to the ground where physical strenght give much more advantage Made me realised that I have been wasting my training in a blind alley by trying out randori in full force.
Humiliating thing is that if I relax my arm, I get thrown far more often. Not only that, I was humbled to realised that I was finding it easiler to throw that weaker opponent because he was faithfully following our coach’s instruction by relaxing his arm and trying out as many throw as possible in randori which made it easier for me to throw him. When he had go at me, he was far more formirable. But I’'m still better than him though. 
Correct way to do randori whether it is standing or groundwork randori is to do it by 80% of force. Trying out randori like competition in regular training is huge waste of your time because you and your opponent would be locked into hold and never being able to try out techniques.
And I stress it again. Trying to obtain the correct feeling for technique, which in tajiquan’s case involve slower performance of form because of its emphasis on the correct body alignment and in case of judo, doing kata cooperatively which any good coach will tell you to do, might seems useless at first but it is far quicker way to improve your ability in medium and long run.
