When you orgasm, your body releases chemicals that lower cortisol. A quick 10 minute jerkoff session before bed won't matter much but if you're watching porn all the time (gooning) then you'll have a prolonged lowered cortisol impact. Low cortisol over longer periods of time causes brain fog, fatigue and muscle weakness. You start to feel "flat" emotionally. This will have negative impacts in all aspects of your life.