Sex is a physiological need, like food, water, shelter.

It clears and releases the mind of that fervent, natural desire, allowing for better concentration.

Plus, it can be terrific cardio!

Masturbating does the trick when one is busy, but doesn't address the underlying issue of a physiolgical need for human, sensual contact, which lifts the spirits, awakens the brain, and is ever-energizing.

Like the ad for Viagra (or the other) showing a newly confident man -- it's often easy to read a man's level of sexual satisfaction instantly.

I had two grandfathers up until recently.  My maternal one cheated on my Grandma continuously and complained, at 84, that his girlfriend at the time (who died not too long afterwards) would only give him sex once a week.  He died at 96.
My paternal grandfather was widowed when he was 49 and, considering his wife had been fighting cancer for a few years before she died, he probably wasn't getting much nookie.  In fact, from what I've heard about the woman (her name was Dora and she died before I was born), I doubt he got much sex even when she was well. Anyway, I would odds he never had sex again until his death at 104, yes I said 104.  
Who knows, if he had gotten as much as my other Grandpa he might still be alive today at 106.

is the mental consideration of wanting to live longer.

Sex is a mainstay for me right now (though not the only) but still the desire to live long is just as if not more important than the physical ability.

Who would want to kick the bucket before having that big time next Saturday night with Sexy Sally!

...tell us something that even a dumbass like me already knew.  Duh, sex makes us live longer? Let's see:  Does it get the heart a pumping and move the blood around?  Does it improve one's mental and emotional outlook on life as well as their physical needs?  Duh, I don't know.  Let's spend a year and a half a quarter mil to find out.  The sad thing is:  I'm not joking.