Studies have been shown that if the penis isn't exercise enough that it will lose its capability. A resent study has also show that impotence can be a precaution for a stroke or heart attack, that means bad circulations.
I have seen articles that say that it would be wise to have at least one good hard-on a day and morning hard-ons don't count.
With all that said....I would love to be able to have sex everyday instead of masturbating, but realistically that isn't up to me alone. My wife has the other say on that....

...which sucks. And I'm not going to cheat....
With all that said....I think its a natural form of simulation and the only thing, usually, holding someone from masturbating usually is their religion. Again that is your personal chose and I can respect that. That's why I will never cheat on my wife