Different people have different reasosn for saying yes or no. Some say it is to focus, and that after hard training you can use sex as a reward for your hard work. For the military, let's just say i was told by my co that if you are going out on a long op, like say recon and would be in the sh!t, that you will be thinking self preservation and thinking about love, family, etc, and you don't need to cloud your mind. "Do a good job, come home, and fuck her brains out".
the benefits are that semenal fluid is a great way to expell toxins as well because they can pool up there.
on the downside they say the release of endorphins makes you lazy tired and relaxes you too much. i assume everyone here has gotten laid, so you all know right after, you pretty much could give a shit about the world splitting in two, you just wanna sandwich and a nap. get laid before going to the gym, you'll probably be a little tired or not as focused. I'd hate to think the guys at the gym are so pumped because they all have blue balls. i'd hate to be in the shower and have ronnie coleman take me down because he likes my sweet ass and could not resist anymore. yeah i have a great ass, it's a national treasure, my girlfriend wishes hers was this nice. lol
we did have a thread about this that one ounce of semen taxes the body like losing an ounce of blood.