Various groups recommend exercises like that (and various "clamps") with the intention of being capable of stopping the release of matter from the body. Sadly, this misses the point. One should not be stimulating the energy to the point where the body cannot contain it. White sexual magic is the process of transforming the energy and raising it up the canals of the spinal column. That is the opposite direction from exiting the sexual organs.

So, in synthesis, if you are practicing in an upright and chaste way, you do not need those exercises.