One thing I've become sure of is that needling sensation is usually part and parcel of a good treatment. The aim of a skilled practitioner is to create particular sensations and reactions in a patient, based on their situation. For example, if someone is weak and cold, the ideal sensation should be one of a spreading warmth. If there is an obstruction in a channel, there should be a sense of movement in that channel in order to re-establish proper flow, and so on. The idea that a point is 'good for headaches' for example, is I believe flawed. Any point will only bring about beneficial change if it is needled correctly, which involves deliberately attempting to elicit specific sensations, some of them quite strong.
In my experience patients will generally tolerate strong sensations happily if this is explained to them beforehand. The treatment process becomes more interesting and satisfying for both parties as particular reactions are sought through needle manipulation by the practitioner, and feedback from the patient. The strength of the sensation will depend on the situation and the patient, and I always endeavor to keep things within the an individual's tolerance levels. There are certainly times when I aim for minimal sensation - for example, when the patient is obviously nervous, or they have a weak constitution. At other times - for example when there is muscle tightness in a robust patient - they will often feel the achiness and muscle twitches as a positive sign of change (as I do).
As with any treatment, the most important thing is to strive to do what is needed at the time for each individual.