I completely agree that, on a resisting opponent who is moving all the time its not as easy to apply as a technique of the one inch punch.
The reason it exists however is that it teaches you correct body allignment and power derivation so that you can punch without a wind up, and without telegraphing. It basically teaches you to punch with as much power as possible from the position you are already in, or your hands are already in.

And you said it: an opponent will try to limit your joint movement, so in that case it would be very usefull if you knew how to generate power with little joint movement.
In any case i am not claiming that it is the all-powerfull chi ball that its built up to be, but certainly usefull within the principles of economy of motion and speed

It is useful if the art pretty much centers around it. Taiji for example uses it all the time, it doesn't matter what part of your body makes contact with theirs, energy can be directed (and redirected) to that point in any direction. You "sense" the openings, so you would never use it unless there was no doubt you could. Real Taiji applications are quite brutal, because like all other internal arts, you are not only using your explosive energy, but you are "sucking them in" and redirecting their own force directly into your explosive force. Of course the more compassionate ones just redirect their energies away, but in reality, it should not be away, but into the ground (face first if need be).

Bagua for example, will allow you to use this type of energy from various angles, even ankward ones, not just linear ones.