That type of physical contraction is only necessary if the male is in immediate danger of losing control of his sexual energy. One should avoid getting to that point anyway.
In the previous era, there were many techniques like that, and they were needed during those times. Of course, many traditions continue with those antiquated techniques. But now in the Aquarian era, they are outdated and unnecessary. Now, we go directly to the point, which is to totally relax the physical body, and work with the energy in the vital, astral, mental, etc. You cannot do so if you remain totally absorbed by physical sensations.
"Do not worry; cultivate the habit of being happy." - Samael Aun Weor