It depends on how its done. I once had a white belt Taekwondo student come up to me and complain that she wasn't able to practice her hand grabs on her son, who is a black belt. He knew what she was going to do and applied all his strength against that motion. She said she wasn't sure she was doing it right if she couldn't use it on him.
I explained to her that she wouldn't be able to. What she would do, if she knew more techniques, is to go the other direction. If your attacker is preventing you from going across their body to break their grip, you go around their body. However, she hasn't been taught that yet, and shouldn't be expected to know it. Heck, she hasn't even been taught the techniques that go in the other direction! At her level, she's learning pieces of the puzzle that will come together later. Her son, the black belt, should have been using passive resistance (make her have control of the technique, but don't fight her on it), because she's not yet ready to figure out those transitions and modifications to make it work.
In my Hapkido class, which is completely focused on hand grabs, this is how it works:
As a white belt, you learn drills such as what I saw posted in the other Kenpo thread. There are 27 drills, mostly which deal with wrist grabs. You have 8 cross-arm grabs, 6 straight-arm grabs, 4 two-on-one hand grabs, and 4 double hand grabs, as well as a few others. In a different order, you have 6 Z-locks, 5 variations of a standing armbar, 5 Q-locks (I don't know if that's the actual name for it), 4 v-locks, and 3 figure-4s. There's also a half-dozen "finishers" to get some to tap out.
As a higher belt, you add in more, which up through blue belt cover different scenarios (grabs from the back, grabs while kneeling, punches, kicks, etc). Red and black belt start to go back through the various scenarios with more advanced techniques. But let's look a little bit about the journey:
- At the white belt level, you have 27 hand grabs, and the prescribed technique is basically gospel. If you're supposed to take them down and then apply a wrist break, and they fall on their back instead of their stomach, you're scratching your head trying to figure out which way to turn, or what to do with them, since your technique has "failed".
- At the yellow belt level, if I take a white belt technique, I should be able to see them fall, go through a list of finishing moves in my head, select one, and then apply it.
- At the purple belt level, I should be able to figure this out through subconscious thought instead of conscious thought - i.e. I see them hit the ground and know where to go.
- At the orange belt level, I should know which way to modify my technique based on how they're falling, instead of after the fact and how they fell.
To look at a specific example, let's say the technique is to apply a Z-lock, take them down to their stomach, and then break their wrist. But they fall on their back instead. I need to know how to switch from a wrist break to an elbow break with the proper footwork and angles.
So I can definitely see how it can work, in the right context.