Your penis will shrink if you don't use it. If you are not circumcised, you increase the risk of getting phimosis if you don't play with foreskin regularly.
Risk of prostate cancer increases without regular masturbation/sex.
You will recall that under the Clinton administration, the US's surgeon general had produced a report that showed the advantages of masturbation and recommended masturbation. She had to be fired because purinatical elements in USA society would not accept such a recommendation. (Despite Clinton being very sexually active)
Consider the progress made during victorian era where masturbation was banned. Consider the programm man made once masturbation was no longer banned. Electricuty, computers, man on the moon, the internet etc. There a a definite corrolation
Masturbation is good. And it is also good for the economy (increased consumption of toilet paper, increased purchases in porn materials etc etc). It is also a good cardio vascular exercise, especially when you get it to last over 10 minutes instead of just 30 seconds. If you get it to last an hour and get all sweaty in bed, it is also a good exercise to lose weight.
So lets put this in short form:
if you stop masturbating:
-penis smaller
-foreskin problems
-prostate cancer
-you get fat
-less healthy
-you go nuts.