Some benefits to quitting masturbation/quitting porn/semen retention include:
1) Deciding you don't need to constantly tug your junk and ejaculate will allow you to focus easier on your goals. You probably herd of boxers/fighters not having sex before fights, or people claiming athletes decreasing in performance after getting a gf/wife, or dudes saying "no sex till I close the deal". Thats why.
2) Ever notice how after you fap or have sex, you are tired? The physical energy involved is a part of it, but its mostly the ejaculation. Your nutjuice is your energy. The less you nut, the more energy you'll have for anything. You will notice it most if you are exercising/weight lifting.
3) Sure it is a stress reliever, but is it really? Smoking is also considered a stress reliever, but after a while I'm craving another one and what happens when I can't? I get more stressed. Sometimes the thing relieving your stress is also causing your stress.
4) Guys have reported their acne problems and/or balding/hair thinning problems improving after extended semen retention. The science behind it is the skin is being deprived of nutrients/enzymes that you are ejaculating. Also, acne/balding can come from stress, hence #3.
5) You will re-sensitize yourself and get less picky when it comes to everyday women, because there are a lot of beautiful women walking the streets, we just don't notice them because they don't have a supermodel's face which is blasted with the semen of 10 dudes. I've gotten desensitized to the point where only certain actresses and scenes would pop my wood. Then I abstained from fapping/browsing sites for one week and when I was browing one page of the most unflattering girls on Javjunkies daily update and I was already full on rock hard raging boner.
6) If you like a girl, she knows and the girls that see you interact with her know. Its the vibe we give off. Its our nature as guys to just want to spread the seed. Once we have control of that, girls will pick up that vibe too, and you won't always be the one having to chase, they will chase you too now.