...even theoretically? I've taken ITF TKD for years, and we do a few, but the only situation I can think of where it might be of some use is a jump spin side kick, which will let you do that kick at closer range than if you leave your front foot on the ground while spinning. I guess, theoretically, if you barrage your opponent with multiple kicks, jump kicks can be alarming and disorienting and unexpected.
- You've guessed part of the equation. They are shocking to anyone who you manage to pull one off on.
- In addition, if the jump is going forward, you add all of your forward weight and momentum to the kick.
- Jumps also allow you to reach higher targets than you might be able to reach standing.
Jump kicks telegraph quite a bit, and so are easy to get out of the way of.
In a self defense situation, you stand to fall and hurt yourself if the ground is uneven or littered with debris, or if you just execute the landing poorly.
As Sean Duggan mentioned, I described pretty much the entire taxonomy of Taekwondo kicks here. It's long, but useful to read if you're a student of Taekwondo:
As for jumping kicks, you can perform these a number of ways. First is by themselves, just jumping straight up. In this case, you're not traveling. You'll just do the jump kick and then land. Second is to add a hop to it in order to travel across the floor. You can add a step or two to it before jumping, also, if you have the distance. And lastly, you can add multi-kick combinations to your jumps. In this case, you can perform one or more techniques on the ground before jumping, one or more techniques in the air just after you've left the ground, and one or more techniques in the air as you're coming down.
A popular example of a jumping multi-kick combination is the whirlwind kick, which is a spinning inside-to-outside crescent kick with one leg followed immediately by a jump outside-to-inside crescent kick with the other leg before the first leg is put back down on the ground. You can take that whirlwind kick and do it again and again, chaining them each together into one long sequence, maybe adding traveling by hopping out as you jump. It can be effective with the proper timing and in the right situation.
But the question is how does this benefit you vs. not jumping.
I discussed something similar here:
What I noted there was that the most useful techniques "apply in the greatest number of situations, and they seem to be the quickest, easiest, and safest to do."
By this definition, jumping kicks are not among the most useful techniques. This is because they have a limited number of situations where they can be used, they are not as quick as other techniques that don't involve jumping, they're definitely not easy to do, and they're not as safe to perform.
And yet, jumping techniques still are useful in some situations. And to a large degree, being able to use them reliably depends on the practitioner. Repeat them enough and get very skilled at not just performing them but also knowing how to time them right and use them during sparring, and they can be useful in many situations. But not most situations.
So to me this comes down to how you should prioritize your time during training. From the beginner to late-intermediate levels, you should spend most of your time working on kicks (and punches, etc.) and combinations that are the most useful. That would be your basic, non-jumping kicks. Everything up to spinning / reverse kicks. Maybe include hopping kicks also. Drill the hell out of those. Get really good at those. And spend a relatively small amount of time on jumping kicks during this time. Later on in your advanced levels, you can work more on jumping kicks, but not unless you've drilled all the other kicks so much that you're nearly perfect at them.
I'm not going to go into the litany of all the problems you might encounter with jumping kicks. Suffice it to say, there are many. In general, they are riskier to perform and require caution.
In Taekwondo, it's often said that this is like a physical game of chess. You have to be thinking 3 steps ahead of your opponent. That means having a plan for when things go wrong. It's like that with any technique, but jumping kicks can go wrong in spectacular ways, which means you need to prepare yourself for all those ways ahead of time.
There are also big rewards that can come from many different jump kicks. They can be powerful, surprising, and lightning fast. These can end a fight. They can also "shield" you from getting hit in some situations, since your opponent might not be able to lock onto you very well, especially if you add spinning and/or hopping to the jumping techniques.
You will learn all about the positives and negatives first-hand as you train. By black belt, you'll be good enough to know you shouldn't use them without careful consideration.
- Increased height - sometimes you have to kick higher than you can from a standing position.
- Ground evasion - If an opponent is striking low, a short hop may take you over that attack so that you can attack them.
- Avoidance of terrain - A short hop over an obstacle or broken terrain can be beneficial
- Startle effect - Many people freeze up when something jumps at them. That may work for a jumping kick as well.
- Closing distance - A hop or jump can close the distance between you and an opponent pretty rapidly.
You may also find some interesting discussion here, where a TKD guy explains the myriad variations of kicks.