questions about masturbation

Hi
I have been reading about taoist sex. Here are a few questions.

1)Why is it some taoist teachers encourage masturbation (without ejaculation), while others totally disencourage it?

2) Does masturbation for a long time without ejaculation use up a lot of chi? In my experience, it seems to be so.

3) Stephen Chang in his book showed the reflexology parts of the penis. Will stimulating the head of the penis too much cause too much heatiness, as it is the heart organ’s reflexology area? Also, is it possible the heatiness can cause hallucinations and schizophrenia(ie, the kidney water becomes low and lacks will power to control one’s thoughts and imagination)?