There is a passage in there somewhere that talks about "spilling one's seed" but I am not a scripture quoter and do not adhere to any religious delusions.
BUT, let me have a look and see if I can find it so you can read up on it...
perhaps
Book of Genesis > chapter 38: Onan?
http://www.christianbiblereference.org/faq_masturbation.htm
As far as I can surmise, Masturbation also sets you up to violate commandment of not coveting another man's wife or property?. Since masturbation and fantasies tend to go hand in hand (lol) there might be some validity in this if you believe God knows your thoughts.
Considering that religion may not dictate everything you do there is opinion that masturbation is good for you.
http://www.plannedparenthood.org/learn/sex-and-relationships/masturbation
This article may have an agenda considering its source (I don't trust Planned Parenthood Organization).
From a scientific angle
On a very basic level, it releases dopamine - a neurotransmitter that activates the 'pleasure center' in your brain, and endorphins that actively decrease your perception of pain. For women, that means it can actually reduce the pain of menstrual cramping. Plus you'll get a surge of the hormone prolactin, which will help you fall asleep afterwards.
Psychology Today says there are mental benefits to masturbation as well.
http://www.psychologytoday.com/blog/stress-and-sex/201401/touchy-subject-the-health-benefits-masturbation
creating a sense of well-being; enhancing sex with partners both physically and emotionally; increasing the ability to have orgasms; improving relationship and sexual satisfaction; improving sleep; increasing self-esteem; improving body image; reducing stress; releasing sexual tension; relieving menstrual cramps; strengthening muscle tone in the pelvic and **** areas; and reducing women’s chances of involuntary urine leakage and uterine prolapse.
The Ultimate Rejection:
When you're masturbating and your hand falls asleep.
. drops the kleenex box to the ground..omg.. I hope not...
..
