I've often questioned the usefulness of forms, but for none of the reasons described above.
The main reason people falsely believe forms have some sort of value is usually listed as "muscle memory". The idea that a move repeated enough times, becomes smoother, or more accessible during an altercation. Repeating a move over and over again in the air will do absolutely nothing for your reflexes or so called 'muscle memory'. In fact, repeating a move or series of moves over and over again in the same pattern and sequence will actually be counter productive to your bodies ability to respond quickly.
This I find to be entirely false. The problem here is that traditional martial arts place a lot of emphasis on technique. I'm doing Taekwondo, which has very difficult kicks that we often practice just against the air. We also spar and practice on targets, but practicing the technique in the air gives us the muscle memory on how to do that technique correctly. Sparring is what helps us use that technique on reflex.
First, there is no TIMING, without a resisting opponent in front of you. Since there is no timing to be had, your reflexes, or response time against a resisting opponent, will not change, increase, or be helped in the least.
I've never seen forms claim to help you with your timing. What they do help you do is learn to move and strike at the same time, maintain balance, and enforce a variety of techniques.
Second, there is no impact, as there is against a heavy bag. So there will be no benefit to your strength, body mechanics, or conditioning. In fact, your body mechanics may become altered in correctly due to the fact that you are not making impact against anything, but merely striking 'air'.
While there isn't impact, you can still tell the people who put power into their techniques from those who don't. Proper stances during the form will help with balance, leg flexibility, and maybe a little with leg strength. Trust me on this: if you're doing a form properly (using proper technique, putting your power into it) you will be winded and sweating real fast. I dread when I have to do all of my forms in class instead of just the one or two we're working on, because by the time I get to the forms I'm working on I'm winded already.
Thirdly, even when shadowboxing (another comparison morticians like to make when making zombies), you never want to repeat the same series of movements to many times in a row! This is a basic rule all boxing coaches are very familiar with. Go to the well to many times and your opponent becomes 'wise' to your arsenal. An example would be a boxer whom always hooked off the jab. After the second attempt he becomes predictable, and easy to set up for a counter attack or knockout. This is why it's important to make sure your athletes shadowbox fluidly. Watch them to insure that they are NOT repeating the same sequence of movements, in the same order, over and over again.
At my school, only the simplest forms involve generic copies of each other, and that's because they are more to teach you how to do forms than anything else. The intermediate forms start to have deviation here and there, and the more advanced you go the more complex the forms become. Training multiple forms also gives you different sets of techniques. Part of the reason katas were created in Karate was to have a small set of forms that teach you all of the techniques of Karate, meaning all of the techniques had to be included in the forms (otherwise they wouldn't serve their purpose). While I agree sparring and freestyle practice are better at teaching creative thinking, I would not say that anything but the most basic forms are "repeating the same move over and over again."
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Now, where I question the usefulness of forms, specifically in Tae Kwon Do, is how different forms are from sparring. The stance is different (deep stances in forms, narrow stance in sparring). The hand position is different (hands tucked at your side in forms, hands in a guard position - either similar to a boxer or held at your sides - in sparring). There is a much larger focus on hand techniques in forms, and sparring is mostly kicks (could be 100% or it could be 60%, depending on how much the fighter likes to use his/her hands). Forms largely teach blocks while sparring teaches avoidance and counter-attack. The footwork is different (forms are mainly steps, sparring is a lot of bouncing and skipping).
However, one thing I've realized is that our self defense drills support deeper stances and use more traditional techniques, and seem very effective (granted, I haven't tested this theory). I think it would be more effective than trying to trade blows with an opponent. These techniques are very aggressive and tend to go for target areas that are not allowed in sparring (neck, face, groin, knees, etc). Forms give us better practice at the stance and technique than 1-step sparring drills, but the 1-step drills help us with timing and accuracy. Sparring helps us work on our timing, even if everything is different about how we do it. I think it all works together to give us a nice variety of training that would combine together in an actual self defense situation.
Similarly is the question of Taekwondo Gymnastics; those flashy kicks and flips that have no business outside of a demonstration or an action movie. The 540 kicks and 720 kicks, or the flashier version of actually effective kicks. On the one hand, if you can do a good 720 kick, it probably means you can do a good tornado kick. On the other hand, working on the tornado kick itself is probably going to lead to more direct results on
that kick. While it's possible to debate if these flashy moves are worthwhile, I say "they're fun to try" and ignore the question of their usefulness
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TL;DR version: I think forms have some benefits, even though sometimes I tend to think I'd rather be sparring or kicking a bag.
