Question

what is semen ? what is useful

Answer 1

 

"To be able to realize God, one must practise absolute continence. Sages
like Sukadeva are examples of urdhavreta. Their chastity was absolutely
unbroken.
There is another class, who previously have had discharges of semen but
who later on have controlled them. A man controlling the seminal fluid for twelve years develops a special power. He grows a new inner nerve called medha nadi (the nerve of memory). Through that nerve he remembers all, he understands all.

Loss of semen impairs the strength. But it does not injure one if one
loses it in a dream. That semen one gets from food. What remains after nocturnal discharge is enough. But one must not know a woman.

The semen that remains after nocturnal discharge is very 'refined'.  The Lahas kept jars of molasses in their house. Every jar had a hole in it. After a year they found that the molasses had crystallized like sugar candy. The unnecessary watery part had leaked out through the hole."

Answer 2

It is a fluid secreted by the glands of male reproductive system .It helps to carry the sperm to the vagina-cervix-fallopian tube