wow.. sex is always the hottest topic, no matter where, even in a personal development forum!
As someone has mentioned, the urge of man to have sex is the nature's way of preserving a specie.
Masturbation is a natural way to release our build up urge to have sex and when there are no immediate partner available.
It is healthy, although it can becomes addictive.
It is definitely a good training on our mental discipline to control it, especially when the urge comes, it attacks your thoughts directly!! But I have to say it is very difficult in the beginning, as I have tried this 30 days challenge myself before. I failed miserably the very first attempt after just a few days.
Subsequently I find it easier if I occupy my thoughts with other things and exercise regularly.