In the medical perspective, semen is viewed as a biological substance secreted by males in order to fertilize the eggs of the females via the sperm-egg union process. By definition, semen is an organic fluid, also known as seminal fluid, that usually contains spermatozoa, and physiologically secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals to fertilize the female ova. Science and society have limited semen's function to this and nothing more. Well, what else could be the function of men's semen aside from procreation?

Image Source
With all due respect to the human anatomy and ethics of science, medical technology has always focused their attention in determining, monitoring and enriching the quality of semen secreted by men. Fortunately, recent studies and sociological explorations have expanded the knowledge of men towards the other uses of semen aside from procreation. Different uses of semen have been uncovered in this discussion; however, some of them are inclined to scientific proofs, while others are purely mythical.
Before we begin, please be advised that all these contents are solely for medical and sociological discussions.
Semen Can Induce Allergic Response

Image Source
Absolutely considered and validated by medical science, rare cases of women have been recorded to experience hypersensitivity towards seminal fluids. This condition is medically known as human seminal plasma hypersensitivity. Symptoms may either be localized or systemic depending on the body response of the woman's antigen and the amount of seminal fluid that entered the body. Manifestations include vaginal itching, redness, blisters, and sometimes, even difficulty of breathing. Oh my... this is really disturbing.
Semen is Believed to be a Potent Source of Energy

Image Source
From a sociocultural point of view, semen has been attributed to potential energy source according to Chinese medicine and Chi Kung theory. According to Chi Kung theory, energy from many pathways/meridians becomes diverted and transfers itself to the sexual organs during sexual excitement. The theory proposes that upon expelling of semen, certain energy from the man's body is also being released. This explains why men feel weak after releasing their sperm.
Magical Use of Semen

Image Source
From Strickland-Bosavi region, Papua New Guinea, the tribe called Etoro believes that semen provides sexual maturation among the younger men of their tribe. Anthropologists have branded the tribe with notorious remarks of homosexuality. According to their practice, younger men of their tribe need to drink their elders' semen in order to achieve sexual maturity. To them, semen possesses the manly nature of the tribal elders, and in order to pass down their authority and powers, young men of their next generation must drink their elders' semen.
Taste of Semen is Related to the Food Men Eat

Image SourceSemen's taste varies from bitter to sweet. According to Bodansky in his book, To Bed or Not to Bed (2005), some women like the taste of semen and others cannot stand it. The semen of different men varies depending on their diets, their cleanliness, and other factors they have control over. Weird, but this can actually be true since the nourishment that the semen contains largely depend on what the body absorbs from diet and other external factors. According to Alman in his book, Doing It (2001), caffeine and red meat, for example, can make the semen's taste acidic or bitter.
Women's Anti-Depressant Drug

Image Source
Sex is a emotionally satisfying and absolutely to boosting activity; however, I just can't comprehend the fact of semen becoming an anti-depressant drug for women? Sounds absurd? Well, according to article of R. Persaud of NewScientist.com, semen literally makes women "happy". Gordon Gallup, a psychologist in the State University of New York, led a study dividing 293 female students into groups according to the frequency of condom usage and happiness assessment results using Beck Depression Inventory (BDI) scale. The result of the study reveals that women whose partners never used condoms scored the average 8 on the BDI scale, while those who often used them acquired the score of 10.5 and those always used condoms scored 11.3. Undoubtedly, those who never had sex with their partners yet scored 13.5. Indeed, semen can actually cause such mood change since it contains different mood-altering hormones, such as testosterone, estrogen, follicle-stimulating hormone, lutenizing hormone, prolactin and various types of prostaglandins
Semen is Nutritious

Image Source
Many couples have posted so many questions about the nutritional content of semen. Somehow, scholarly resources do not provide sufficient information regarding this topic. However, after thorough research, Johnson and Everitt in their book, Essential Reproduction (2000), and L. Paget in her, How to Give Her Absolute Pleasure (2000), reveal that a man's semen really does contain high nutritional content. In one typical ejaculation (approximately one teaspoon), semen already contains 150 mg of protein, 11 mg of carbohydrates, 6 mg fat, 3 mg cholesterol, 7% US RDA potassium and 3$ US RDA copper and zinc. Indeed, the semen of a man contains high nutritional value.
Swallowing Semen is a Good Birth Control Strategy

Image Source
Fellatio or the swallowing of semen has been linked to the concept of birth control. Initially, medical science did not take this issue seriously since logic would explain that fellatio and oral sex are unquestionable birth control means. However, according to N.V. Benokraitis (1996) in his book, Marriage and Families, as well as Askmen.com, fellatio is rumored to delay fertilization and strengthen the immune response of vaginal secretion against the male's semen.
Hmmm... although, I don't think I'd reconsider believing to this. In fact, according to Gagnon and Simon in their book, Sexual Conduct (2005), fellatio only brings metaphors of dominance and male gratification. There is no single scientific proof that can validate the birth control benefit of fellatio.
Though Shall Not Run Out of Semen

Image Source
Last but not the least, men literally can never run out of semen. Very true, since men only needs at least 15 minutes to replenish their semen right after ejaculation. According to TheSite.org, there is no need to have sex or masturbate to ejaculation for health reasons. The body can happily cope with unused sperm, with no impact on or sex drive. Meanwhile, in the study conducted by American scientists in Newscientists.com among 30,000 men over eight years, those that ejaculated most frequently have had significantly less chances of getting prostate cancer.