Trying to have a baby is one important reason to have sex. There are other important reasons to have sex regularly, according to this article in Forbes: "Is Sex Necessary?" Refer to this article whenever someone preaches to you that the only proper reason to have sex is to have babies. The article is based on a study that correlated overall health with sexual frequency:

Queens University in Belfast tracked the mortality of about 1,000 middle-aged men over the course of a decade. The study was designed to compare persons of comparable circumstances, age and health. Its findings, published in 1997 in the British Medical Journal, were that men who reported the highest frequency of orgasm enjoyed a death rate half that of the laggards.

Here are some of the health benefits to having sex on a regular basis:

• Reduced risk of heart disease
• Weight loss, overall fitness
• Reduced depression
• Pain relief
• Less frequent colds and flu
• Better bladder control
• Better Teeth (go read the article)
• Keeps prostate healthy (I've heard this from my own doctor)

Humans also use sex to bond with each other, shown by the fact that humans are "unusual in our continuous practice of sex, which is a direct consequence of our concealed ovulations." Whenever someone preaches that using sex to maintain social bonds is "unnatural," feel free to remind them that humans aren't the only primate to use sex to bond. Check out the behavior of our cousins, the bonobos.