You know after you wank your did kinda, shrinks a little? If you strap on an extender right after you cum, you won't get that shrinkage. That's what i do anyway if i cum while edging or clamped girth work etc.
Masturbating will not increase the size of your penis, or change any aspect of your physical appearance. However, masturbation does have a number of physical and mental health benefits, such as relieving stress and physical tension. Many people masturbate to relax, to feel good, and it can help some people fall asleep.