The reasons Sperm Banks exist are:
1) Like myself, I wanted to preserve my Sperm while I was still young and potent. I do not want to have children at this time.
2) Artificial Insemination - Many couples cannot have children through routine sex, so sperm and eggs are extracted and a baby is made in a Petri dish and inserted into the womb of the mother.
3) Some women, such as Lesbians, never want a man, but still want children.
4) The use of a surrogate mother.
5) To extract or pre-determine a specific sex (male or female).
6) To insure a healthy baby, free of disease, genetic disorders, and STDs.