It would depend.

On clarity of thought definitely negatively, but if it is innate to me, the drive for sex, then I would've been negatively impacted by it either way.
The base issue is the sexual drive, and porn that you waste time for is a derivative.
Porn in itself is tempting and wasting time, distracting because I am a human which was built for it as the main goal of life.
I like a good fap to pregnant lolis getting raped by shotas but the extent to which it impacted me is only wasting leisure time which I don't think I would've spent productively anyway.
If not fap then I would probably drink instead which leads to the same lack of productivity only giving the benefit of temporary joy not by means of achieving something as a response that productivity is encouraged as nature intended, than simply abusing mechanics of how I was built teaching me that productivity is not the answer for joy if I have a hand and a dick.
These two are polar opposites. How good it is only depends whether you achieve joy by productivity or counterproductivity, I would diagnose it as an exploit of a human body.

Funnily enough I type it in a post orgasm fap break.
After all what do you do after cumming? I go to /b/.