That's like asking "Is water useful?" It's a nonsense question, because there is no absolute answer: it's always dependent on the situation. Define the situation and you can arrive at an answer; refuse to define the situation, and it's just mental masturbation.
On another thread, from which this on was spawned, it was stated that pain will lead to incorrect Aikido technique. Therefore, it is argue on that thread, techniques should be done painlessly. Maybe I assumed that everyone would have understood where this question is coming from. What is your opinion, does experiencing pain during the practicing of a technique help or hinder learning Aikido?