To my stand point of view and my knowledge, not other doctors or specialist, if you do it more so often, it will cause physical damage to your genitals, like soreness or infection. Also every ejaculation, you will lose a great amount of minerals needed for your body. Those are the cons.
For the pros of it, like you said, it can prevent you from STD while you have your satisfaction. Some studies shown it can help to prevent cancer, but can cause your life span shorter.
Sum it up, after a period of time, that will become your habit and your desire will increase and masturbation won't satisfy you any more, so you have to look for greater thing.
To me, it isn't a good idea to ever start it unless you're already old enough to know the cons and pros of it.