This is a post I just put on the nofap reddit and I thought I might share it here as well:
I just had a thought.
From things like yourbrainonporn and reuniting.info I've come to see how porn works in the primitive brain: it's like your own personal harem, which you keep fertilizing and fertilizing.
Those sites put up your biological conditioning as a sort of supervillain that has to be fought. They say us males are programmed to fertilize as many receptive females as possible to spread our genes.
And, you know, that sounds reasonable at first, until you think about the possible ramifications of this: What would happen if you were actually to fertilize hundreds of receptive women? Think about it.
They would, of course, all get your children. Now, even if these women could somehow take care of these kids without you, there'd be a problem: you're now stuck with hundreds of children that have your genes. In small communities - the kind that used to be common - that's not a very good thing. In fact, it's a really really bad thing. These kids would be more likely to have incestuous relationships, simply because there'd be no other choice of partners.
So I think evolution built a mechanism into us to prevent this kind of thing. It's not obvious because it happens subconsciously: our genes actually make us less attractive to the opposite sex if we orgasm a lot, because the primitive part of us actually needs genetic diversity so that our own genes have a bigger chance of survival. I think by exhausting ourselves sexually all the time, we voluntarily let other men have a go at it so that our own kids will then have a better chance at finding suitable, genetically diverse mates.
And this, my friends, is where I think the nofap benefits really come from.