Sex results in the entry of sperm cells of male into the vagina of female.
Sperm cells travel into the uterus and one of them fuses with the female gamete, ovum, resulting in the formation of a zygote, in the fallopian tube. This process is called as Fertilization.
Fertilization is one of the major events of sexual reproduction.
The zygote, thus formed, develops gradually and gives rise to a baby.
Hence, coapulation (sex) is important for human reproduction.