Many things.
Porn numbs your dopamine receptors / reward centers. It acts as a sort of drug, no different than cocaine or heroin. Many people have no Idea how numb they are to things relative to their natural state.
Excess ejaculation lowers testosterone as well. Each time you ejaculate releases a surge of Prolactin which by extension, also lowers testosterone. The research Is fairly limited here, but we do know that abstaining for a week raises testosterone levels by 44%. Testosterone Is not the only factor though. Excess ejaculation appears to have a profound effect on androgen receptors, which are what determine the effectiveness of testosterone. The research here Is relatively limited though considering the massive Importance of the subject, I tend to think due to political issues / potential conflict of Interests.
But, yes. To Beyond the 'drug' like effects of excess porn, one only needs to look at all the beneficial / unique compounds found In sperm..It would be silly to think that expelling that amount of energy would not weaken us In a multitude of ways, particularly with women, especially when abused. Our Immediate hunger for food, lack of mental clarity and Increased susceptibility to other drugs, substances, alcohol to fill that void Is a tell tale sign of this. Not to mention our reduction of game / proficiency with the opposite sex.
Sex is a bit different than a solo orgasm because It's more of an exchange of energy. So those effects are not as substantial.
Anyways, all that said..there are many layers to It. But, there's a reason why so many high level athletes like Muhammed ali have abstained prior to their fights. Not to mention greats throughout history, spiritual and religious figures. As a martial artist and someone who's boxed for a long time, abstinence can Improve your game / focus and fire multiple fold.
Sexual energy Is quite a powerful thing and most people don't realize what they're wasting and how It's affecting them because living In this numbed state has become the norm.
But, yes..to put It simply, abstain from porn and ejaculation for a month and see how your game with women improves. It's quite dramatic In many cases.