I suppose as a mental & emotional challenge it might hold some attraction, sort of a self-exploratory thing. But as many have noted here, if your body doesn't like it, wet dreams will set you back to square one, so will you really have abstained for 40 days? I mean, you could start this, but as soon as you have a nocturnal emission, you might as well throw in the (trick) towel, and clean up the mess.
You also risk a painful case of blue balls, especially if something should excite you, like seeing a hunk at the gym, or a naked guy in the locker room, or what used to do it to me, a lengthy kissing & petting session. And worse, at 18, wet dreams don't just happen in your sleep. A hormonal young man can ejaculate spontaneously in his shorts, hands-free, if he's sexually stimulated enough, and has gone "dry" for long enough. And you thought only old guys wet their pants...
[The phenomenon of blue balls is disputed by some, but the considerable pain I myself felt when sexually aroused for too long without release was real enough to me, when I was a young man right until about 30. The likely cause is excess production of seminal fluids that distend some of the internal structures, particularly the seminal vesicles, vas deferens and epididymis, the pain then radiating outward.
Hence it would feel like someone had kicked me in the balls. And even my finally shooting wouldn't provide immediate relief, like when you empty your bladder, because the soreness of tissues not designed to stretch would take time to fade away, sometimes several hours in my experience.
My advice for a young man, therefore, is to keep your "pipes" flushed out on a regular basis. I really think it's what Nature wants you to do.]