Piercing the tongue has ancient antecedents, but it wasn't until the 1990s and the rise of body-modification culture that tongue piercing became widespread. Piercer Elayne Angel is often credited with popularizing this particular piercing among both men and women. Why a person gets a particular body part pierced is often a personal, idiosyncratic decision, but there are some common reasons and misconceptions that can be addressed.
Certain ancient and tribal cultures pierced their tongue for ritual purposes. Aztec and Mayan art depicts this practice, and a central Australian tribe called the Aranda still perform these piercings to mark the initiation of a shaman. Piercing the tongue or any other part of the body may be done as a way to face fear of pain, to mark a transition in life or to claim and customize your body as your own.
As popular as tongue piercings are, they do carry some risk. Aside from the risk of infection that comes with all piercings (particularly oral piercings), tongue piercings are known to cause significant wear on tooth enamel, especially if the bearer "plays" with the jewelry by running it against the back of his teeth. Teeth can even crack eventually because of this habit. Tongue piercings may also contribute to receding gums, if the piercing is pushed repeatedly against the front teeth. Many dentists actively discourage tongue piercings for this reason.
Body piercings should never be considered temporary---they are permanent body modifications that often leave scars, marks or other alterations to the body. That said, tongue piercings are among the easiest piercings to "retire." Once the jewelry is removed, the hole will close up quickly. A mark may or may not be left behind.